Biodiversity Net Gain Assessment

Last updated: November 2024

Author: Rob Lambert

Editor at Arbtech, Rob is a content specialist who manages our ecology and arboriculture services copy to ensure it is accurate, up to date, and insightful for current and future clients.

Your Complete Guide to Biodiversity Net Gain: Metrics, Plans and Costs

Now a part of UK legislation, biodiversity net gain (BNG) is set to become a mandatory consideration for all development projects in England, with very few exceptions. It acts as a planning condition and policy requirement of planning consent, causing a significant impact on the decision-making process of local planning authorities as they determine whether planning permissions are granted or refused.

As a result, delivering BNG will become an integral part of almost all planning applications moving forward in the eyes of local authorities, and developers will be required to factor in a consideration to improve biodiversity as part of their pre-development plans.

What is Biodiversity Net Gain?

Biodiversity net gain is a concept whereby the state of biodiversity in an area is improved following the completion of land and building development work. In any proposed development, a biodiversity net gain consultant will ensure that the plot of land is preserved as much as possible, retaining various habitat types, avoiding biodiversity loss and protecting ecological features of strategic significance to encourage developers to continue their project in an environmentally considerate manner. However, in some circumstances, there is no alternative but to safely relocate inhabiting animals and destroy or move veteran trees and plant life that may be an obstruction to the development.

As a way of counteracting the potentially negative impact of a development, mandatory biodiversity net gain insists on not only replacing elements of the area that were removed due to the development but increasing the overall state of biodiversity by 10%, enhancing habitats and delivering net gain in the process. Development biodiversity is a consideration that will stand as an integral part of the planning process for all projects now and in the future – a policy requirement that local planning authorities will expect from developers.

Anyone in charge of a planning project will need to factor in mandatory biodiversity net gain, including in multiple developments such as independent, commercial and even nationally significant infrastructure projects on big and small sites. Throughout this process, the developer will be required to understand statutory biodiversity credits and the current biodiversity metric, and recognise the ecological importance locally of development biodiversity value and how it will need to reach a certain bracket from pre-development to post-development, increasing by a secure measurable net gain of at least 10% and maintaining for at least 30 years.

Biodiversity Net Gain Principles

According to the Chartered Institute of Ecology and Environmental Management (CIEEM), there are ten key good practice principles of biodiversity net gain that, when followed accordingly, should achieve BNG and habitat enhancement. A responsible body such as CIEEM providing further information and expert advice on implementing BNG correctly within a suggested structure enhances public access to the planning obligation and works to encourage developers to continue with developments despite the new planning condition.

Mandatory BNG principles:

1. Utilise the mitigation hierarchy to minimise the impact on biodiversity
2. Eliminate negative impacts on biodiversity that cannot be offset elsewhere
3. Involve all pre-development and post-development stakeholders in forming mandatory net gain solutions
4. Understand the potential risks and variable factors to achieve biodiversity net gain
5. Determine a suitable method to secure a better state of biodiversity
6. Ensure the best possible outcomes from biodiversity net gain
7. Offer nature conservation that exceeds the BNG requirements
8. Focus on generating long-term environmental benefits from biodiversity net gain
9. Cover all areas of sustainability, incorporating economic and societal factors
10. Communicate all biodiversity net gain outcomes with complete transparency

Check out CIEEM’s biodiversity net gain principles for a more thorough explanation and further detail of these considerations.

Examples of Biodiversity Net Gain

Depending on the specific plot of land and all components within it, different outcomes for delivering biodiversity net gain may be possible. For instance, if there were no animal species or trees on the development site, the process of offsetting and increasing the level of biodiversity value and mandating net gains at the required standard for biodiversity in the area following the completion of the proposed development project could be relatively straightforward.

However, if a protected species was present on the site, for example, the British standard licensed ecologist would need to ensure that they won’t be disrupted as a result of the development. At this stage, a protected species survey may be required to obtain a full picture of the inhabiting species and guarantee their safety despite the development. Alternatively, if it was inevitable that they would be disturbed by the development, causing a biodiversity loss, the ecologist would need to find a way of safely relocating them elsewhere. They would then need to ensure that the site had the same standard of biodiversity pre-development before building on that standard by an additional 10% upon development completion.

For mandatory biodiversity net gain to be successful, applicants of planning permissions must work within the guidelines of the mitigation hierarchy. In simple terms, the mitigation hierarchy works as a suggested structure that determines the most suitable course of action on development sites, all while protecting present animal species, enhancing habitats, and delivering net gain calculated using the current biodiversity metric.

Within this planning system, the top priority in the first instance of the mitigation hierarchy is to completely avoid harm or disruption to natural elements in the area. If this isn’t possible, the ecologist will be required to develop mitigation measures that minimise adverse impacts such as carrying out the development in ways that don’t infringe on certain areas or providing extensive training to construction staff for working on a site that houses animal species and delicate plant life.

As a last resort, in circumstances where disruption or destruction to animal habitats and plant species cannot be avoided, the ecologist will need to offer expert advice on ways of compensating for recognised biodiversity losses, such as by relocating or creating new animal habitats and suitable locations for plant species on-site, off-site or a combination of the two. Despite the fact that the changes may be made outside of the habitat site, as long as the 10% net gain increase is achieved, the rules of biodiversity net gain allow this approach to be taken.

Benefits of Biodiversity Net Gain

In a study published in ‘Conservation Letters: A Journal of the Society of Conservation Biology’, the initial benefits of biodiversity net gain were analysed. An observation from this study was based on the use of statutory biodiversity credits. In any land development project, if certain natural assets on the site need to be moved elsewhere or destroyed, the developer will be required to compensate for these biodiversity losses as well as increase the state of biodiversity by an additional 10% through the use of biodiversity units to determine biodiversity value, even if it means meeting the criteria off-site rather than on the specific plot of land.

Introducing a biodiversity tariff within the biodiversity net gain policy was partially utilised as an incentive for retaining irreplaceable habitats and plant life on-site, and to encourage people to get involved in local habitat creation, enhancement schemes and any initiatives from other organisations that aim to preserve the environment, undertake habitat creation on a larger scale, develop land that grows natural capital, or even combat climate change via, for example, remedying water and air pollution. Fortunately, the society claims that their sample saw a low percentage of purchased biodiversity units, as 95% of the units were delivered on-site or on neighbouring plots of land.

Due to the importance of the effectiveness of the policy, the study looked at whether the sample indicated a measurably better state of biodiversity post-development. Despite original aims to generate an upturn in biodiversity by an estimated 20%, the sample actually saw a reduction of 34%. However, the net loss was compensated by wildlife habitats that met the required increase outside of the site, or environments with far more quality and longevity, even if they didn’t necessarily reach the expected increase.

Additionally, it could be advisable for land developers to aim above the 10% biodiversity net gain increase, particularly as it would be near impossible to maintain the same level of biodiversity on land that was previously agricultural, greenfield or green belt; overachieving would ensure successful BNG delivery.

The Department for Environment, Food and Rural Affairs (DEFRA) claim that an estimated 75% of biodiversity net gain enhancements will be made on-site, but the feasibility of on-site BNG delivery will be determined by the number of units the plot of land started with and the specifications of the site and project.

Merely projecting an improved state of biodiversity as a whole in the future isn’t quite as effective or reliable as ensuring that biodiversity will be enhanced on the plot of land as a direct result of the development. However, compensating for an inability to improve biodiversity on the site as a last resort does mean that developers can at least meet the required biodiversity value overall and sufficiently deliver BNG by contributing to the cause elsewhere.

Evidence from the study indicates that biodiversity net gain may face alterations during the early teething period after being only recently launched. It could be a common occurrence for developers to enhance biodiversity in other parts of England due to being unable to do so on their own site, but these results suggest that it is in fact an effective method of improving the environment.

For example, a trial of biodiversity offsetting was carried out in six pilot areas across England between 2012 and 2014. Scotland and Wales weren’t incorporated as the policy was only intended for England, with these other countries holding their own suggested structure for calculating biodiversity, benefitting the environment and appeasing local authorities. The results were promising, with Warwickshire standing out through frequently trading BNG credits for off-site enhancements.

Why is Biodiversity Important?

The concept of biodiversity is important for a number of reasons, and it applies globally regardless of country. Key benefits that biodiversity offers include:

• Enabling the production of raw materials
• Enhancing the Earth’s visual appearance
• Facilitating a scientific understanding of the natural world
• Offering recreational activities such as birdwatching, camping, fishing and hiking
• Providing jobs for farmers and other agricultural vocations
• Supplying oxygen and water to the ecosystem

Considering the vital nature of biodiversity, the concept of mandatory biodiversity net gain is a defined, structured and regulated method of ensuring all of the above factors are encouraged and supported over future years. It also applies to all development proposals, causing a universal approach from the UK government.

Through rolling it out in the same way as any other form of government policy, any potential uproar with various key stakeholders is prevented. Not only does this include individuals who are proposing development projects privately or commercially, but also formal institutions that want assurances over an increase to the biodiversity metric such as DEFRA, Natural England and the British Standards Institute (BSI).

Biodiversity Net Gain Legislation

Former Environment Secretary Michael Gove on behalf of the UK government announced the concept of biodiversity net gain (BNG) originally back in December 2018 before introducing the new Environment Bill in October 2019. It then became the Environment Act after achieving royal assent and being passed into law in November 2021. Previously, the UK had existing protections over the environmental impact of development projects on the environment under the EU’s policies. However, these planning policies no longer applied to the UK after Brexit came into effect on 31^st December 2020.

What is the Environment Bill?

The government announced the concept of the new Environment Bill 2020 in the spring statement as a legal structure for protecting the environment in a development proposal following the UK’s departure from the EU as a result of Brexit.

In the new Bill, aims included developing effective conservation covenants, improving water and air quality, increasing recycling, protecting wildlife species, recalling products that breach environmental standards, reducing plastic waste, regulating chemicals that could potentially harm the environment, and using resources more efficiently. As a result, biodiversity net gain served as one of several core policies with long-term effects on ensuring numerous habitat types are secured for at least the next three decades.

What is the Environment Act?

In November 2021, the Environment Bill achieved royal assent, passing into UK law and becoming the Environment Act 2021. Part 6 on nature and biodiversity covers all other areas of biodiversity net gain across two core sections.

The first section covers biodiversity net gain for planning as part of applications for planning and nationally significant infrastructure projects, as well as more detail on site registers and biodiversity credits. The second section focuses on the primary objective of biodiversity net gain, highlighting the importance of on-site and off-site habitat enhancement and conservation over a period of at least 30 years in all development projects, and offers an overview of biodiversity net gain reports specifically produced to cause measurable improvements to the state of biodiversity.

Is Biodiversity Net Gain Law?

Within the Environment Act, the concept of biodiversity net gain and operating within the biodiversity metric on new developments has instantly turned into a consideration that the relevant local planning authority, developers, architects, land owners and anyone carrying out a project must adhere to.

Although the Environment Act 2021 is lawful, its policies – with mandatory biodiversity net gain included – weren’t ever expected to be fully integrated until at least the year 2023 as it goes through a two-year transition period. Many local authorities, however, enforced the new National Planning Policy Framework (NPPF) in line with detailed guidance from DEFRA and Natural England and applied a 10% biodiversity net gain requirement on each new development proposal in preparation for it becoming the norm. An example of this is Cornwall Council, which stated back in March 2020 that they would be requiring a minimum biodiversity net gain of 10% on all major applications.

With a growing number of local planning authorities stipulating biodiversity net gain as a general condition of seeing planning permission granted, it was advisable at the time that anyone planning a development project considered the requirement early as part of pre-development preparations and kept it in mind across the planning process all the way through to the post-development stage. Even if the local planning authority wasn’t enforcing the rule, integrating the conditions of the biodiversity net gain policy requirement would avoid impacts on their initial planning approval application that could have risked it being refused and prevented potentially costly delays to their development schedule.

Biodiversity Net Gain Timescale

The process of passing the Environment Act 2021 into law and initiating biodiversity net gain required several steps over a lengthy period of time.

Below, we outline a clear timescale of the introduction of biodiversity net gain into UK law:

• December 2018: Environment Secretary Michael Gove announces the concept of biodiversity net gain, citing it as a “commitment to protecting and enhancing our natural world [that] can go hand in hand with our ambition to build more high-quality homes.”
• December 2018 – February 2019: DEFRA holds a consultation on biodiversity net gain to allow affected parties to have their say.
• March 2019: Chancellor of the Exchequer Phillip Hammond presents the spring statement to parliament, with biodiversity net gain included as one of several policies.
• July 2019: DEFRA publishes a report on the results of the consultation, detailing the feedback they had and responses to individual comments.
• October 2019: The government announces the Environment Bill, replacing environmental protection policies that would no longer apply as a result of Brexit. Biodiversity net gain was included as one of several core components of the bill.
• January 2020: The Bill undergoes the first reading in the House of Commons.
• February 2020: The Bill undergoes the second reading in the House of Commons, as well as passing a programme motion, money resolution, and ways and means resolution.
• March 2020: The Bill passes the committee stage in the House of Commons.
• June 2020 – January 2021: The Bill passes multiple programme motions, as well as a carry-over motion.
• January 2021 – May 2021: The Bill passes the report stage in the House of Commons.
• May 2021: The Bill undergoes the third reading in the House of Commons before undergoing the first reading in the House of Lords.
• June 2021: The Bill undergoes both the second reading and the committee stage in the House of Lords.
• September 2021: The Bill passes the report stage in the House of Lords.
• October 2021: The Bill undergoes the third reading and consideration for common amendments in the House of Lords before undergoing the consideration of Lords amends and programme motion in the House of Commons.
• November 2021: The Bill undergoes the consideration of the Lords’ message in the House of Commons and a second consideration of common amendments in the House of Lords. It then achieves royal assent, earning the title of the Environment Act 2021 and passing into UK law.

A two-year transition for introducing biodiversity net gain into the plans of developers, new developments and the requirements of local authorities followed, working towards a national rollout in Autumn 2023.

In addition, July 2023 saw the release of a list of actions that the local authority can take to prepare for the new planning requirements.

The actions included the following factors:

• Harnessing an understanding of rules surrounding habitat creation or enhancement
• How the new planning conditions could intertwine with the corresponding local plan
• The local authority’s duty to sustainable development and green infrastructure
• What would need to feature within a biodiversity gain plan to see planning permission granted

Why was Biodiversity Net Gain Brought In?

Despite an emphasis on the minimum requirement for architects, developers, landowners and planning consultants, biodiversity net gain is only one small part of the Environment Act. The concept has been raised several times over the last few years, and as such, there are multiple reasons why it was introduced.

As previously mentioned, one of the primary purposes of biodiversity net gain is as a consequence of the UK’s decision to leave the European Union. Without association to the EU and as an independent country, the UK is no longer obliged to follow European environmental regulations, meaning a new form of legal framework was needed to ensure that the UK enhances, preserves and protects the natural environment, particularly during nationally significant infrastructure projects.

Though only a small part of a larger strategy, biodiversity net gain plays a vital role in all of the key aims of the legislation. Flourishing ecosystems mean cleaner air and water, and well-tended green spaces not only contribute significantly to mitigating climate change but also add relative value to the economy, both locally and nationally. Healthy natural environments are almost universally desirable places to live and work, so it is likely that the fiscal value of land – and the developments thereon – will increase in tandem with the ability to incorporate biodiversity improvements.

Is Biodiversity Net Gain Bad News for Developers?

While it is understandable that land developers, architects, planners and any other professionals involved with developing land privately or commercially might see this renewed push for environmental protections and enhancements within biodiversity net gain as yet another hurdle to jump in the pursuit of planning consent, it is probably better to view the 10% mandatory BNG requirement as an investment.

Contrary to popular belief, the UK government don’t want to stand in the way of development at any stage in the process, either in pre-development planning or as the project is undertaken. They recognise that there is a critical housing shortage and understand the challenges faced by the construction sector. However, nature has, however, been in decline for decades, with a report from 2019 claiming that 41% of UK species had decreased in abundance, while only 26% saw increases. Due to this, mandatory biodiversity net gain (alongside other sections of the Environment Act) has stood as a pragmatic solution that prevents further damage to the environment, promotes progress towards a stronger state of biodiversity, and ensures that the project increases a habitat’s distinctiveness.

The data also shockingly indicates that the abundance of the UK’s priority species had declined by as much as 60% since 1970. Consequently, the UK has some of the worst biodiversity figures in the world, leading Dr Andy Purvis of the Natural History Museum to claim that the UK has ‘led the world in degrading the natural environment’. It is important to note that he also cites the Industrial Revolution as the starting point of this movement away from a purely natural environment. But as the state of biodiversity wasn’t properly maintained, bringing mandatory BNG into law should reverse the damaging effects of the past fifty years. As such, the emphasis on increasing biodiversity and enhancing habitats through biodiversity net gain – either on the specific plot of land or across the UK as a whole – could enhance the natural environment to a standard beyond its original condition.

The arrival of a strategy that actively promotes developments while enabling you to simultaneously incorporate biodiversity improvements, enhancing habitats and the natural environment, and halting developments that are ambivalent or harmful towards it was inevitable. In fact, a biodiversity net gain approach that unified the goals of various key stakeholders benefits all parties without meaning the environment – or the projects of property developers – are treated as collateral damage.

Biodiversity Net Gain Consultation

Prior to officially announcing the intention to mandate measurable net gains for biodiversity, the government response came in the form of a consultation. It gave developers, local planning authorities, non-governmental organisations, other organisations of relevance such as utility companies, and the general public great opportunities to provide feedback on implementing biodiversity net gain (BNG) on a long-term basis following the brief overview of the planning policy originally referenced in the spring statement.

Government Response to Biodiversity Net Gain Consultation

Following the conclusion of the consultation, DEFRA published a report in July 2019 that detailed their findings and changes that would be made based on the feedback they received.

As a result, the government announced a response to the feedback, with the report indicating that:

• All compensatory habitat sites and similar such sites will be listed in a publicly available national register for wildlife habitats, and purposeful habitat degradation prior to applications for planning conditions will be prevented
• District-level licencing will not be mandated and there won’t be a new tariff on the net loss of biodiversity
• Every development will be subject to the application of the mitigation hierarchy, but minor development projects will face a simplified overall process
• Exemptions will be made for brownfield sites under certain criteria, but none that are broad or beyond existing development and household exemptions. Irreplaceable habitat sites and marine developments will also be exempt, but there has not yet been a decision on statutory protected sites.
• Local authorities will receive funding following the transition, assist with delivering net gain and control planning policies on locally designated sites
• Net gain will be set at 10%, with a transition of implementing biodiversity net gain over the outlined two-year transition period and the effects of biodiversity net gain designed to last a minimum of at least 30 years
• Smaller development sites will be within the jurisdiction of BNG, but minor residential developments should have a lower net gain and longer transition arrangements
• Sites containing Areas of Outstanding Natural Beauty (AONB), Sites of Special Scientific Interest (SSSI) and other similar site categories may be treated differently on a case-by-case basis.
• The Environment Bill will insist on local decision-makers agreeing on BNG plans with developers; conservation covenants will be legislated
• The Local Nature Recovery Strategies (LNRS), the Nature Recovery Network (NRN) and the Natural Capital Committee (NCC) will advise on the application of BNG in new developments
• The original environmental impact on biodiversity will be minimised through efforts to improve environmental mapping

Biodiversity Net Gain Metrics, Calculations and Assessments

The introduction of the concept of biodiversity net gain (BNG) has concerned many developers, with worries that it will ruin existing or future developments once it is fully rolled out. With this in mind, you will want to know how BNG is going to affect your planning application.

Below, we’ve detailed how the biodiversity metric works, offered advice on how mandatory BNG units are calculated using the biodiversity metric and how you yourself can carry out the process of calculating biodiversity net gain and explained how Arbtech can help you to remain within the rules of relevant UK legislation.

Biodiversity Net Gain Assessment

Under the new legislation, you will need to submit and receive approval for what is known as a ‘biodiversity net gain plan’ (or sometimes simply referred to as a ‘net gain plan‘). Once the Environment Act 2021 becomes more frequently adhered to as part of the law, you will need a net gain plan to meet planning requirements for your development. At this point, it is important to stress that this is none negotiable – no plan, no planning permission.

The legislation also stipulates that planning approval should only be granted on the condition that your development can enhance the biodiversity value of your site to a better state. Specifically, the value of the site should be enhanced “in a measurably better state than it was beforehand” (Cornwall Council, 2020). In some ways, this has always been the case, or at least the concept of aiming to improve biodiversity value during development projects has for the last few decades. The existing NPPF even paved the way for this back in 2012.

However, the crucial difference here is the word ‘measurable’, with measurable improvements making the process more defined and therefore easier for a land developer to successfully achieve BNG. Based on this information, you will be wondering how exactly the local planning authority case officer will make a biodiversity net gain measurement, what it will be calculated using to determine an enhancement of biodiversity value, and how you can achieve biodiversity net gain on your development site.

It will likely come as a relief to you to learn that the process for measuring biodiversity net gain is not based on an arbitrary decision by your local planning case officer. There are several ways to measure biodiversity value using a different biodiversity metric. The primary tool that you will currently encounter, however, is the DEFRA biodiversity metric 4.0 – a tool designed to measure biodiversity gains and losses as the result of proposed developments. It replaces DEFRA biodiversity metric 3.1, 3.0 and DEFRA biodiversity metric 2.0 which were previously used.

Using the biodiversity metric 4.0 tool, planning officers can determine the net gain or biodiversity loss of any proposed project, enabling you to receive evidence that, all being well, your land development project has seen a biodiversity gain of at least the required 10% increase between pre-development and post-development. For more information, Natural England offers further detail in an in-depth overview of biodiversity metric 4.0 to deliver BNG.

Biodiversity Net Gain Calculator

The process of calculating biodiversity net gain to secure measurable net gains using the DEFRA biodiversity metric 4.0 requires a limited number of factors. They are:

• Type of habitat, both on and off the site
• Size of habitat parcels in hectares or kilometres
• Condition of each habitat parcel
• Locations (if they are nature priorities of local importance)

Further information in regards to irreplaceable habitats present on the specific plot of land will be detailed based on the results of the relevant habitat survey undertaken pre-development. Findings from a habitat survey can then be used to gauge the habitat’s size, type, condition and location into a biodiversity metric 4.0 score. The resulting net biodiversity gain score will then be measured in what are known as ‘biodiversity units‘ or ‘biodiversity credits‘.

The government website even provides a biodiversity metric 4.0 calculation tool for determining your biodiversity unit score in a way that translates to the standards of your local authority.

For additional information on BNG metrics, the latest DEFRA metric and the difference between each version, check out our guide to the biodiversity metric.

How to Measure and Calculate Biodiversity Net Gain On and Off-Site

Assessing mandatory biodiversity net gain on or off-site will need to take place at the point that planning conditions are applied for, allowing for recent, deliberate harm to the biodiversity value of your site to be considered. As a result, local flora and fauna won’t be harmed to artificially reduce the biological value of land and make the 10% net gain requirement easier to achieve. If this is found to be the case and the work or other activity on the site took place without permission, the consequences of those works will not be taken into consideration when assessing the value of the site.

At the outset, you will probably need a preliminary ecological appraisal – a baseline walkover ecological impact assessment that includes an opportunity to identify priority habitats as part of the biodiversity metric. Then, once the development work is complete, further surveys will be performed and your site will be scored again to determine whether biodiversity net gain has been achieved. A ‘net gain’ in biodiversity will be successful if the score is higher after the development than it was before the development. Under the Environment Act 2021, your site will have to achieve a net gain score that is at least 10% higher. It also insists on the net gains for biodiversity realistically remaining in a better state for at least 30 years.

How to Deliver Biodiversity Net Gain of 10% on Your Site

When it comes to achieving the required 10% mandatory BNG increase to enhance the site to a better state, you have a number of options. That said, regardless of the route you choose to take, the habitats you create or enhance as part of biodiversity net gain must be maintained for at least 30 years. Local planning authorities will also be permitted to stipulate protection over and above this.

During biodiversity net gain assessments, the overall biodiversity value will be split into two categories: hedgerow and habitat. Although not mutually exclusive, each biodiversity net gain unit is assigned a relative value, giving comparable development value between pre-development and post-development caused by a balance of an ecologically rich habitat and a habitat of relatively poor diversity.

What is a Conservation Covenant?

Another option for making biodiversity net gain work would be through the option of a conservation covenant. A legal agreement between the developer and a responsible body, a conservation covenant protects natural sites and acts as a reliable safeguard for rural communities and existing habitat quality. Even after the original landowner sells or parts with the land, conservation covenants remain indefinite and continue to protect natural habitats and prevent avoidable habitat loss.

In practical terms, a conservation covenant is only likely to make further development of the land and the overall land management process more difficult, operating in a similarly wary manner as biodiversity net gain. Additionally, along with putting assurances on the retention of relative biodiversity value in new development projects, landowners receive benefits from opting into a conservation covenant, such as receiving offsite compensation, financial assistance and tax benefits for any form of conservation work carried out on the existing site, even if the works could gain biodiversity net and lead to being suitably maintained for at least 30 years.

A step forward towards the universal implementation of biodiversity net gain on development proposals occurred in July 2023, where gov.uk launched the official application process to get involved with supporting conservation covenants on new development projects, and as a side effect, allowed them to protect biodiversity and minimise negative impacts on habitats in a way that can be realistically achieved on-site.

What about Offsetting and Biodiversity Credits?

Ideally, the corresponding local planning authority will be looking for you to demonstrate biodiversity net gain ‘on-site’. The exact mechanisms you can use to achieve this will then depend on all sorts of things including – but in no way limited to – location, condition and past and present habitats. But, generally speaking, factors like planting or seeding native tree and shrub species, allowing wildflowers to flower, and managing eutrophication (an over-abundance of nutrients – common on many urban development sites) will go a long way towards enhancing biodiversity.

In some circumstances, however, significantly enhancing the biodiversity gain of a site simply isn’t possible. It doesn’t necessarily mean that it is the end of the road for your development, as it doesn’t automatically mean that your planning permission will be refused by the relevant planning authority. Instead, the local authority will take a close look at your planning application and may still grant it if you are able to deliver sufficient biodiversity net gain in the form of off-site habitat enhancement. It is worth noting that the local planning authority does not have to deliver this off-site net gain with their land. As the developer, the net gain is technically your responsibility, even if it requires the purchase of more land to facilitate your compensatory or mitigation measures.

To give a dramatically simplified example: if your site had a pre-development biodiversity value consisting of 100 biodiversity units, to satisfy your planning obligation to the local authority under the Environment Act 2021, you would need a post-development score of at least 110. For anyone who is left with no choice but to take an approach to development that involves biodiversity offsets, gov.uk now offers more than just a first glance of how metrics assign the value of a site through guidance on credit prices.

You may also have the option to ‘purchase’ statutory biodiversity units or credits from or through funding schemes that will generate the equivalent number of units elsewhere. Concerns over credits have been raised here, however, as there is potential for total habitat destruction in place of what may previously have been preservation, almost entirely contradicting the purpose of biodiversity net gain.

It is also worth considering that, by involving an ecological consultant at the design stage and having them present in the right places of the planning process, the likelihood of you needing to deliver net gain in the form of off-site enhancements to achieve the aims of mandatory biodiversity net gain will be significantly reduced if not entirely eliminated.

Do I Need to Deliver Biodiversity Net Gain?

The Environment Act 2021 states that a two-year transition period will be ongoing until November 2023, making the implementation of the law patchy and similar to the great crested newt district licencing scheme. As a result, each local authority is likely to take a slightly different biodiversity net gain approach to this new mandate as they use the transition period to create and refine a planning system that is suitable to the region they cover. That said, it was announced in September 2023 that the universal enforcement of the policy would be delayed until January 2024 before then being delayed once again until February 2024.

Net Gain: The Key Exemptions

As mentioned above, there is a list of exemptions that are not covered by the 10% biodiversity net gain target. Until the Environment Act is universally utilised, the policy could be subject to change. But for areas governed by existing legislation such as ancient woodland or conservation areas, for example, the rules are likely to stay the same.

The Environment Act also appears to offer significant latitude to many local planning authorities when it comes to agreeing on what constitutes an acceptable biodiversity net gain plan in terms of the mitigation hierarchy and corresponding offsite compensation measures. Although the 10% biodiversity net gain requirement is non-negotiable, the degree and form of acceptable off-site biodiversity enhancement appear to be up to the local planning authority to determine with the developer on a case-by-case basis. Additionally, factors such as the site of special scientific interest are entirely excluded from the biodiversity net gain assessment planning system and the requirement to deliver BNG – something the local authority should be aware of as and when it is applicable.

Biodiversity Surveys, Plans and Reports

The involvement of a specialist ecological consultancy like Arbtech from the design stage will lend credibility to your application, reduce the cost of compensatory measures by maximising the existing biodiversity net on your site, and minimise the overall risk of your planning application being refused by the local authority.

We recently worked with a client to prepare a pre-development biodiversity net gain assessment and plan using the relevant biodiversity metric for the property team of the Royal Borough of Windsor and Maidenhead.

When to engage an ecologist if you think that off-site BNG is going to be necessary

Even though the Environment Act isn’t strictly followed by every local planning authority until 2024, it is prudent to start thinking about what it means for your development now. Not only could this prevent any issues with local planning authorities that have already begun to follow the rules of mandatory biodiversity net gain prior to 2024, but also prepares you for when the rules are enforced from 2024 onwards.

If you are at the Royal Institute of British Architects (RIBA) plan of work stage 0-1 now (feasibility), for example, then by the time you get to stages 3-4 (submitting a planning application), the later stages of the transition period where some councils will undoubtedly look for strict application of the scheme could affect involved local plans on development sites and development proposals that pay no attention to biodiversity net gain.

In some cases, the local planning authority will ask you to demonstrate biodiversity net gain prior to November 2023 or the newly-expected February 2024 launch. At least four local planning authorities have already adopted a policy that closely focuses on net gain ahead of the national rollout. It is highly likely that more will soon follow suit, primarily catering to the policies of the Environment Act, calculating biodiversity net gain, checking that the biodiversity metric is taken into consideration, and ensuring that there is some form of consideration over new habitat creation and efforts to enhance biodiversity.

What should you do about Biodiversity Net Gain?

If you’re unsure of how the biodiversity net gain mandate will affect your planning application, the best thing to do would be to contact your local planning authority immediately. Then, if they indicate that your development will be significantly impacted, it would be strongly advisable to involve an expert ecologist as early as possible to check that your plans will suitably achieve BNG.

If, for any reason, you are unable to gain the necessary clarity from your local planning authority, Natural England, DEFRA or the BSI should be able to provide you with accurate information. As all of these public bodies, regulators, organisations and authorities cover the entire country, however, your local planning authority would be more relevant as they will focus solely on the area you are looking to stage a development project.

Biodiversity Net Gain Plans

As previously mentioned, in order to have planning permission accepted by your local planning authority, you will need to prove that you have taken the correct measures as part of an effort to achieve biodiversity net gain through booking an ecologist to develop a biodiversity net gain plan. Based on an ecologist’s findings in a BNG assessment, the net gain plan will determine natural elements that could be lost as a result of the development project and effective measures for mitigating these outcomes.

Our team has been helping people meet their ecological and planning obligations to secure planning permissions for many years now. It is something that we are experienced and qualified in, so you can be sure that the ecologist who comes to your site to develop a net gain plan has the ecological expertise you need for writing reports specifically produced to deliver BNG.

The subject of mandatory biodiversity net gain is a crucial one in current and future development projects, so we are on hand to offer the strong support you need to reach the required bracket to mandate net gains on your site. We also share the same priority as you – making sure that your application passes the planning process of the corresponding planning authority.

How much does a Biodiversity Net Gain Plan Cost?

Our British standard biodiversity net gain assessments cost from £469+VAT, with the cost expected to vary depending on the scale and intensity of your site and development.

The price for the purchase of biodiversity units and credits as part of an offsetting scheme will be in part determined at the local level, and as with most things in life, demand and supply will probably need some time to reach an equilibrium where it is cost-effective for developers to uptake the various schemes.

For a biodiversity net gain quote that is relevant to your plot of land and requirements, it would be advisable to get in touch with us directly.

Biodiversity Net Gain Guidance

For matters as important as achieving planning approval, it is crucial that you gain biodiversity net gain advice and guidance from genuine experts who offer good practice over ecology and an understanding of other issues such as existing legal implications. Every single one of our ecologists is licenced and educated to bachelor’s or master’s level. They know their stuff, possessing a wealth of expertise in local and national ecological networks to guide effective environmental management based on the corresponding local planning authorities.

With such an array of skills including writing reports for delivering BNG, operating within the appropriate biodiversity metric, understanding the full picture and each specific duty of the planning process, and implementing BNG effectively, each of our ecologists is fully capable of decision-making and providing pragmatic solutions and ecological expertise for big and small sites. We also ensure that the further information we provide on the biodiversity gain requirement and delivering BNG for a development site is in line with new guidance based on the latest standards.

Our demanding in-house training programmes are designed to keep our knowledge of mandatory biodiversity net gain up to date and in line with current rules, regulations and standards, as well as the latest information from Local Nature Recovery Strategies (LNRS), the Natural Capital Committee (NCC), DEFRA, Natural England and specific local planning authorities. In turn, when something like the Environment Act 2021 causes the goalposts of biodiversity gain to shift significantly, they take it in their stride and adapt accordingly.

Likewise, our licensed ecologists are knowledgeable in a broad range of areas, simplifying the process to encourage developers who need help with planning impactful changes pre-development to prompt an appropriate increase in biodiversity net gain, managing development biodiversity through the planning process, ensuring the biodiversity value reaches the necessary level based on biodiversity present after the development and remains there for at least 30 years. We can also provide an overview of any otherwise confusing factors such as the use of biodiversity metrics, on-site and off-site habitat enhancement, gaining biodiversity credits, or dealing with an active conservation covenant.

The majority of our 80-strong team is home-based, allowing your Arbtech biodiversity net gain specialist to provide crucial knowledge of the policies and procedures your local planning department use to make planning decisions regardless of where you are situated. Not only does this mean that you get the guidance over specific local planning authorities you need to secure planning permission, but you also get it the first time and fast – or your money back.

Choose Arbtech for Expert Advice on Biodiversity Net Gain

Need an assessment to demonstrate measurable improvements to biodiversity and successfully gain biodiversity net on your site as part of your development proposal?

If you do, or even if you simply want to develop a better understanding of certain areas such as the mitigation hierarchy, credits and units, biodiversity value, the current biodiversity metric, a conservation covenant or marine net gain and how BNG could affect a marine development, Arbtech is here to help.

We’ve worked with numerous developers and landowners on bigger and smaller development sites who have needed help to calculate biodiversity net gain and successfully achieved net gains for biodiversity to appease local authorities under the planning condition.

It can be an understandable concern that you will be unable to increase and retain biodiversity value and ensure that it is maintained for at least 30 years post-development. However, with our help, we can offer strong support, and fulfil an important biodiversity duty through our ability to deliver biodiversity net gain assessments in the pre-development stage, satisfy local planning authorities, and obtain planning permission.

Call us today on the number above, fill out the quote form on this page or visit our ‘contact us‘ page to see all of our great opportunities for getting in touch with us about biodiversity net gain and other ecological and arboricultural matters, and you will be able to discuss further detail of your development proposal with one of our friendly team and arrange a suitable time for us to visit your site and advise on implementing BNG.