Biodiversity Net Gain in Nationally Significant Infrastructure Projects

The Role of BNG in NSIPs

Through the introduction of mandatory rules for nationally significant infrastructure projects (NSIPs), the way the UK handles development and environmental protection has undergone a significant shift. With the arrival of biodiversity net gain (BNG), the primary objective has become to balance economic growth with ambitious biodiversity outcomes that deliver nature recovery across England.

For developers working their way through the planning system, integrating BNG means ensuring that large-scale developments leave the natural environment in a measurably better state than it was before. Following extensive stakeholder feedback and a new consultation, the government published an official government response detailing the transitional arrangements for the NSIP regime.

Although early proposals suggested different timelines, the finalised parliamentary scheduling confirmed that mandatory BNG for NSIP schemes applies to all applications submitted on or after 2 November 2026. The deadline allowed sufficient time for developers to adapt, offering greater certainty and close alignment across the sector.

The framework for biodiversity net gain is legally underpinned by Schedule 15 of the Environment Act 2021 to bring BNG considerations into the heart of the DCO process. By establishing clear priority guidance, the government aims to provide clarity to promoters, local planning authorities and smaller developers alike.

Certain groups pushed for a higher biodiversity objective, like the RSPB campaign. Despite that, however, the government chose to maintain a baseline BNG requirement of 10%, maintaining alignment with the Town and Country Planning Act 1990 (TCPA). In the early stages of design, the local planning authority can ask for a higher return, as considered alongside the state of local biodiversity.

Comparison Between Standard and Large Projects

While standard projects under the TCPA regime deal with local impacts, major infrastructure projects operate on a completely different scale. When the government was seeking views on the framework, a large majority of respondents supported applying BNG to the NSIP sector but noted that many NSIPs face unique spatial challenges, such as long linear railways, grids and pipelines.

Under standard town planning rules, a minor development or brownfield residential development has a tight and easily defined boundary. In contrast, NSIP schemes often cut across multiple local authorities and involve vast plots of land.

To reflect this, the rules offer distinct delivery flexibility for infrastructure. For instance, while a residential brownfield development must exhaust all on-site options before looking elsewhere, an NSIP can look to the off-site market in the first instance if it better suits the project’s scale.

Standard developments need to operate within complex spatial risk multipliers if units are bought outside of the local council area. For other types of development, the penalty increases costs. In the case of an NSIP, however, the risk multiplier is turned off across the scheme’s footprint, allowing promoters to secure off-site biodiversity gains more efficiently across administrative borders.

How BNG Works Within NSIPs

With BNG for NSIPs, the ecological data needs to sync up with the development consent order (DCO). The system heavily relies on the statutory biodiversity metric to convert habitats into measurable biodiversity units.

To achieve the 10% minimum uplift, the calculation compares the pre-development biodiversity value against the projected post-development biodiversity value. With the help of individual biodiversity gain statements, developers can then see a clear path forward.

The documents act with the same legal authority as national policy statements, specifically tapping into specific NSIP types like energy, transport and water. Each statement outlines the wider benefits required and how to handle specialised infrastructure, giving you a streamlined process even during an intense nuclear regulatory review.

Two-Stage Approval Process

As large-scale infrastructure can take years to design and approve, the government split the BNG approval process into two distinct legal stages, preventing projects from stalling.

Stage 1: The Application Stage

Alongside the main DCO application, promoters need to submit an outline biodiversity gain plan.

The document uses a metric calculation based on initial surveys to show that achieving the 10% target is mathematically and practically viable.

For much larger multi-year builds, developers can submit a phase biodiversity gain plan, which details how the gains will be staggered across different construction stages.

Stage 2: The Pre-Construction Stage

Before any development work or habitat loss occurs, a final biodiversity gain plan needs to be submitted and approved.

Promoters can select a specific discharging authority to sign off on these monitoring proposals and final designs, ensuring a single point of contact rather than chasing multiple local planning authorities.

BNG Boundary and Rochdale Envelope

A common issue in major infrastructure planning is that the exact footprint of the project is not finalised when the DCO application is submitted.

To solve this, developers use what’s known as the “Rochdale Envelope” principle to assess a realistic worst-case scenario.

The Rochdale Envelope is not calculated across the project’s entire order limits (including untouched land). Instead, developers draft a specific BNG boundary plan using specialised BNG boundary metrics. It will then create a smaller area focused purely on:

• Habitats within the boundary line that will be negatively impacted by the works
• On-site plots of land dedicated to delivering BNG habitat creation

Any completely unimpacted habitats or unimpacted areas within the wider order limits are excluded from the BNG baseline calculation by default, protecting developers from paying to improve a habitat included in the boundary that they never actually touched.

Temporary Impacts and Reinstatement

Major infrastructure projects regularly use massive areas of temporary land for construction compounds, soil storage and laydown areas. If the areas are occupied for less than five years, the BNG framework offers a major operational concession.

As long as the developer is enhancing biodiversity by fully restoring the ground to its original state or better within that five-year window, the metric treats the habitat as retained rather than lost. With this, developers don’t need to secure temporary zones under a 30-year legal agreement.

The rule applies to standard greenfield land, low-value fields and urban edge areas, but it explicitly excludes public gardens and community playing fields, and anywhere else under distinct public protection rules.

If a planning project impacts highly sensitive ecosystems, however, the rules tighten significantly. Irreplaceable habitats sit entirely outside of the standard 10% metric calculation, and you cannot destroy one and simply claim to offset it with standard off-site gains.

Delivery Flexibility and Trading Rules

At the point of securing gains, the infrastructure framework offers maximum commercial flexibility, allowing developers to balance on-site habitat creation with the acquisition of off-site market units.

There’s flexibility in where you buy units, but you must strictly follow the biodiversity gain hierarchy and the metric’s trading rules. The rules dictate that you need to replace lost habitats with the same habitat type or one of a higher distinctiveness.

Statutory biodiversity credits are intentionally expensive to avoid distorting the private market and encourage developers to stick with on-site solutions. If a developer runs into a final shortfall because the local market lacks the necessary units, they can access government-issued statutory credits as a last resort.

To prevent third-party landowners from blocking critical state infrastructure by withholding vital offset land, the government has retained the power of compulsory acquisition for BNG purposes, ensuring essential national utilities can always proceed.

Get Help with Biodiversity Net Gain on Your Project

In the landscape of biodiversity net gain (BNG) for nationally significant infrastructure projects, reliable and trustworthy ecological expertise is vital.

Unlike standard town planning developments focusing primarily on local housing delivery, major infrastructure works demand a specialised understanding of how the current metric handles large spatial footprints.

The rigorous accounting applies to both the primary national assets and any associated development that needs to be factored into your boundary calculations, such as access roads, grid connections or construction compounds.

Our team at Arbtech helps to protect promoters by interpreting the latest primary or secondary legislation and existing guidance to identify the most cost-effective and legally secure routes to compliance. The primary objective is to show you how to minimise construction impacts right from the design phase, protecting your planning project from expensive off-site unit liabilities later in the process.

We focus on key areas of your early engineering layouts to reduce unnecessary habitat loss, helping you to map out where you can achieve non-significant gains on-site before committing to large-scale land procurement.

Whether a site has inherited complicated ecological baselines from a previous owner or you are aiming for a higher biodiversity gain objective to align with corporate ESG goals, our strategy is tailored to your risk profile.

Habitat management and monitoring plans (HMMPs) are crucial components in securing sign-off of your DCO. Massive infrastructure assets endure for decades, so discharging authorities scrutinise the long-term legal documents carefully.

Our team has extensive experience with preparing a habitat management and monitoring plan (HMMP) to balance the commercial realities of engineering with the strict legal requirements of restoring nature.

Reach Out for a Free Quote Today

Here’s further information on how qualified ecologists at Arbtech assess your site during the initial design phase to ensure compliance with the BNG requirement.

If your proposed development boundary includes habitats of high distinctiveness, early intervention is needed to address your footprint and mitigate construction impacts. If you then need more help or want to explore voluntary approaches that could smooth your path towards planning approval, our specialist team can assist you.

By remaining closely involved with the biodiversity net gain mandate ever since it was first announced, we’ve built a proven track record for translating otherwise complicated regulations and requirements into actionable development advice in the NSIP context.

For a free quote and any general advice on what you need or where to start, contact our team via our website, over the phone, by emailing us or simply by messaging us on our socials.