An ABC of BNG for NSIPs

This article was first published by Estates Gazette on 9 September 2025 (here).

Biodiversity net gain is the concept, introduced by the Environment Act 2021, to ensure that a defined biodiversity gain objective of at least 10% over the pre-developed biodiversity value of habitat is a condition of planning permissions for new development. The gain is made up of the total of (1) an increase in the post-development biodiversity value of the on-site habitat; (2) any registered off-site BNG allocated to the development; and (3) the biodiversity value of any purchased biodiversity credits. The biodiversity value is calculated in accordance with the biodiversity metric published by the secretary of state.

In England, permissions granted pursuant to planning applications made since 22 February 2024 under Part III of the Town and Country Planning Act 1990 are subject to a planning condition to secure this biodiversity gain objective, unless an exemption applies.

Nationally significant infrastructure projects is the umbrella term for infrastructure projects that are consented by the secretary of state using development consent orders (often referred to as DCOs). They sit outside the Town and Country Planning Act 1990 Act because of their size, impact and strategic significance. They range from energy and waste management projects to super sewers and road tunnels.

In May this year, the Department for Environment, Food and Rural Affairs published a consultation on proposals to extend the biodiversity gain objective to DCOs for NSIPs submitted after a go-live date in May 2026. The consultation proposes that new NSIPs on land (including the foreshore) in England will be required to achieve a biodiversity gain objective of at least 10%. The objective will be defined for each different NSIP type through a separate biodiversity gain statement that will be made by the relevant secretary of state.

Is it all change?

As acknowledged in the consultation, despite BNG not yet being mandatory, many NSIPs are already delivering biodiversity enhancements in some form. This has been driven by a combination of national and local planning policies seeking provision of biodiversity enhancement, identification of opportunities for enhancement by consultation bodies, including Natural England and the Environment Agency, and developers setting their own biodiversity enhancement objectives.

BNG is supported by a robust policy framework already, even in the absence of legal mandates. Government policy emphasises the need for such enhancements. It states that valued landscapes, sites of biodiversity or geological value, and soils should be protected and enhanced, while planning decisions should minimise impacts on diversity and provide biodiversity net gains.

Last year, the examining authority and the secretary of state attributed weight to the provision of BNG in considering DCO applications for the A66 Northern Trans-Pennine project and the A12 Chelmsford widening scheme. While achieving a particular gain in biodiversity is not mandatory for NSIPs, it is not a novel concept.

Challenges of delivering on-site BNG

Delivering on-site BNG for NSIPs still presents several legal and practical challenges. One key difference between voluntary commitments to increasing habitat value and attainment of BNG, as defined by the statutory biodiversity metric, concerns the application of trading rules where habitat will be lost. The biodiversity metric specifies minimum habitat creation and enhancement requirements to compensate for specific habitat losses, up to the point of no net loss. This is likely to pose a challenge for some types of projects, for example linear road and railway infrastructure. These schemes often face physical and legal constraints and rely on compulsory acquisition powers in many cases.

Currently, it is not possible for compulsory acquisition powers to be used to acquire land solely for biodiversity enhancement. If BNG becomes mandatory, a case for the extension of these powers may be made. The availability of biodiversity credits for purchase, and the market price and potential ransom value for land that could be used for the delivery of BNG as defined by the biodiversity metric, are likely to become new considerations.

NSIPs may also come up against the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024. They apply to ancient woodland and veteran trees, for example. A net gain cannot be delivered where there is irreplaceable loss. Instead, bespoke compensation for any such loss must be provided. It will be in addition to the required 10% BNG and on top of mitigation of likely significant environmental effects identified through the existing environmental impact assessment. The stacking of mitigation, BNG and compensation on the same land may be possible, provided there is no duplication, but realistically it is likely to increase land costs.

In contrast, solar farms have found it easier to exceed the 10% BNG threshold. For example, in assessing the East Yorkshire Solar Farm, the BNG achieved by the proposed development was held out to be one of the scheme’s benefits. The secretary of state weighed this favourably in the planning balance and amended the requirement in the DCO to refer to higher percentages of BNG that are to be achieved by the applicant, instead of a requirement of 10%. Similar projects could take the opportunity of managing surplus BNG value by registering a site on the national biodiversity gains sites register and selling biodiversity credits to other developers.

Considerations of off-site BNG provision

In urban areas, on-site BNG is often impractical due to limited land availability. Here, off-site provision may be possible in the form of creating or restoring habitats elsewhere to compensate for losses. A notable example of this is the Riverside Energy Park Development Consent Order 2020, which required the developer to demonstrate payment of sufficient funds to the Environment Bank to secure land on which the necessary biodiversity compensation would be delivered.

The impact of mandatory BNG

While consideration could be given to using compulsory acquisition powers to acquire land needed to deliver at least 10% BNG, the use of such powers raises many concerns. The consultation therefore proposes that applicants will be able to deliver BNG either on-site or off-site in the first instance, to ensure applicants are not incentivised to use compulsory acquisition to further expand their scheme boundaries for on-site delivery. The government’s hope is that with the availability of registered off-site units and statutory biodiversity credits, it is unlikely that compulsory acquisition will be needed.

Other way to support conservation

BNG for NSIPs is one aspect of a wider strategic approach by the government to improve environmental obligations. Recent proposals include the Nature Restoration Fund, which is part of the Planning and Infrastructure Bill. The fund is intended to pool mitigation and compensation funding to deliver conservation at scale where NSIPs could harm certain protected habitats and species (including some irreplaceable habitats for BNG purposes). This shift from project-by-project mitigation and compensation to strategic planning could improve efficiency and ecological impact. However, concerns remain:

Will local communities lose out if biodiversity measures are delivered elsewhere?

Could national scale planning obscure local biodiversity losses?

What powers will Natural England have to manage and direct the fund’s resources?

How will land values be impacted, and how will this affect project viability?

These questions will be in addition to considerations about the future of BNG in infrastructure planning.

Final thoughts

BNG for NSIPs is evolving rapidly, with legal requirements on the horizon and policy already shaping practice. While challenges remain, particularly around land acquisition, urban constraints and effects on land values, the direction of travel is clear. Developers, planners and regulators must progress preparations for a future in which biodiversity gain is elevated from being a consideration to becoming a core requirement.

BNG on brownfield sites

The government’s commitment to BNG continues to evolve, with another consultation launched on 28 May 2025 aimed at refining its implementation for minor, medium and brownfield developments. With growing emphasis on embedding meaningful ecological enhancements, and not just “token” green spaces, the proposals aim to make BNG more practical and proportionate

For minor developments, the consultation proposes either a full exemption from BNG or the introduction of additional exemptions. This reflects concerns about the disproportionate administrative burden placed on small-scale projects, such as those with fewer than 10 dwellings or sites under 0.5 hectares. These developments often lack the scale or resources to deliver significant on-site biodiversity enhancements and the government aims to encourage compliance without stifling development.

A key proposal is the overhaul of the small sites metric, which would be renamed the “low impact metric”. It would apply to sites under 1 hectare with no priority habitats with its use extended to medium developments, defined as those with 10 to 49 dwellings or sites between 0.5 and 1 hectare. Changes include merging habitat categories, adjusting BNG trading rules and digitising the metric tools to reduce reliance on complex spreadsheets.

Brownfield sites also receive a special attention. Often located in urban areas, these sites can contain ecologically valuable habitats, such as open mosaic landscapes which are a combination of vegetations recognised for their high ecological value. However, these habitats are difficult to quantify and protect under BNG metrics. The consultation proposes better accommodation of such habitats to ensure that redevelopment does not cause biodiversity loss.

The consultation also addresses the hierarchy of BNG. For minor developments, it suggests relaxing the requirement to prioritise on-site enhancements over off-site compensation. This may let developers purchase BNG units in broader areas, such as local natural recovery strategy zones, rather than being restricted to local planning authority boundaries.

Ultimately, the proposals aim to balance ecological ambition with development practicality. By tailoring BNG requirements to better reflect the scale and context of each project, the government aims to embed biodiversity into all levels of planning without imposing undue burdens. The consultation closed on 24 July 2025. Its outcome could significantly reshape how biodiversity is delivered across the built environment, so watch this space.