Our information page on biodiversity net gain legislation explains everything you need to know about regulations in relation to BNG, as well as how it was first brought into law in the first place.
Last updated: April 2026
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.
Major development and non-major development schemes affected by biodiversity net gain (BNG) now impact the local authority’s planning decisions. In order for developers to deliver biodiversity net gain, planning law has had to reflect elements of the policy and insist that the BNG requirements are met in relevant permitted development projects.
The biodiversity gain objective aims to improve the condition of the natural environment to a measurably better state following the completion of applicable planning projects. Before a developer can achieve BNG, a biodiversity net gain plan would need to be undertaken specifically for the proposed development.
Outside of the current exemptions such as householder applications, self-build and custom-build development projects, developments involving a transport network and planning applications involving a site no larger than 0.5 hectares in size and containing nine or fewer dwellings, the biodiversity gain condition will apply in many cases, and as such, the planning system has shown consideration to that in legislation.
The concept of biodiversity net gain (BNG) was introduced as part of the Environment Act, making it a consideration that developers, architects, landowners and land managers must adhere to and that local planning authorities must enforce. Although the policies within the Environment Act 2021 are now lawful, the BNG law underwent a two-year transition period between 2021 and 2023, and it only actually became mandatory on 12 February 2024, followed by a small sites version on 2 April 2024.
During the transition period, local authorities set whether or not affected developers would need to stick to the planning obligation at the earliest opportunity, even before it became a mandatory requirement alongside where other existing local policies apply. Since that point, the LPA requirements have involved a 10% net gain for the new rules to be met correctly, and in other cases, specific local councils have asked for a higher percentage to increase biodiversity if it is needed.
As the relevant local planning authority in your area could ask for different parameters to meet the legal agreement, we would suggest researching the planning conditions early and working mandatory biodiversity net gain into your plans as soon as possible. A biodiversity net gain assessment will need to be carried out at the planning application stage, as it will allow for the current pre-development biodiversity value and predicted post-development biodiversity value to be quantified and any deficit between the two to be removed and enhanced by at least 10%.
For more information on how biodiversity net gain became a legal obligation and part of the planning process, we’ve broken down the steps taken to push BNG into the law, urge developers to create biodiversity on-site, and make everyone in planning mindful of their commitment to nature conservation.
Former Environment Secretary Michael Gove first announced the concept of biodiversity net gain in December 2018 before it became a part of the new Environment Bill in October 2019. Once it had achieved royal assent, the Environment Bill became the Environment Act and was passed into law in November 2021, bringing with it multiple policies including BNG.
Previously, developers would support biodiversity in new developments by complying with the EU’s policies. The UK’s departure from the EU, however, meant that applicable policies no longer applied after 31st December 2020. As such, a new development management procedure had to be created, with the new law acting as enforced government guidance to protect and enhance priority habitat.
In preparation for the upcoming departure from the UK at the end of the year, the government announced the concept of the new Environment Bill 2020 in the spring statement as a legal structure for protecting the environment in residential and commercial development projects, as well as a selection of applicable smaller developments depending on the circumstances.
In the new Bill, aims included:
As a result of the Bill, biodiversity net gain would benefit both the ecological value of the environment and a heightened chance of success in the planning application process for the person submitting a proposal to the local council. It also set out clear targets to enhance biodiversity and operate within local development orders, simplified planning zones, transitional arrangements, reserved matters and planning appeals.
After gaining royal assent in November 2021, the Environment Bill became the Environment Act 2021. In part 6, the Act covers nature and biodiversity, with biodiversity net gain specifically explained across two core sections:
The requirement to deliver BNG in applicable development proposals has had an impact on multiple areas within habitat management, land management and general planning. Due to this, more BNG considerations needed to be added to existing legislation and other parts could be added as further information in new legislation.
For all you need to know about primary legislation, secondary legislation and statutory instruments around biodiversity net gain, check out the section below:
At any point that a local planning authority or responsible body requests that biodiversity net gain (BNG) is worked into the proposed approach for a development project, it will be down to you to ensure that it is capably achieved on-site or off-site accordingly. Not only that, but BNG legislation insists on a minimum increase of 10% that will last for at least 30 years. Without it, the information submitted wouldn’t meet the parameters that the local councils use to outline planning permissions.
It is important to understand if the 10% BNG requirement applies to your project, and it may be even harder to tell if you’re working on a custom housebuilding project, phased development, minor development, minerals development or experience any overlap with statutory protected sites such as sites of special scientific interest (SSSI). It could even be that you aren’t sure if you’ll see any issues relating to the mandatory requirement if your site has a low distinctiveness or high distinctiveness of on-site habitat.
As a developer with a development subject to BNG, you can only correctly meet the objective by referring to further guidance from an ecological consultancy such as ours. We can then undertake a BNG assessment, record any important habitats, begin measuring biodiversity value before and after the planned works using the completed metric from DEFRA, create biodiversity gain plans, and execute any other tasks to result in granted planning permission.
The habitat-based approach for generating sufficient BNG units includes a number of methods that could vary depending on the statutory biodiversity metric reading, the measures created using the biodiversity gain hierarchy and/or the species or circumstances of the natural habitats present. For instance, habitat creation such as the addition of bat boxes or habitat enhancements may be able to compensate for the value of habitat lost or add to on-site improvement measures.
Alternatively, however, the mitigation hierarchy might point toward a need for off-site biodiversity gains. At this point, developers can buy off-site units from landowners wishing to sell an application site as off-site land via habitat banks or statutory credits from government-approved sellers. If the project causes too much habitat loss and on-site gains aren’t enough, offsite gains will be the last resort option that enables developers to contribute to the enhancement of land outside of the red-line boundary.
Since the biodiversity gain condition was brought in for local planning authorities to enforce, Arbtech has been keeping tabs on it every step of the way. From the point of it being applicable in specific development projects, we’ve been undertaking onsite BNG assessments and creating BNG plans that ensure compliance over the actions of developers, insist on a universal good practice approach, and propose enough biodiversity enhancements or off-site measures to achieve the mandate.
Every time we help a client with BNG, we run through the three options provided by the mitigation hierarchy and alter our approach to the identified scale and size of your development site and planning project. In addition to assembling a biodiversity gain plan based on our findings, the habitat type in the vicinity and the measures we produce to avoid net loss and grow biodiversity value, we can help with other types of services, such as providing both ongoing management and ongoing monitoring with a habitat management and monitoring plan (HMMP).
A large step in delivering biodiversity net gain is meeting the minimum-level requirement of producing a BNG plan that must be submitted to the local planning authority and approved prior to any chance of obtaining planning consent. If you are dealing with such sites or projects affected by BNG, reach out to our team, provide us with information about your development plans, and allow us to put together a free quote based on your details. We can then choose a relevant date based on your schedule to begin helping you navigate through the requirements.
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