Biodiversity Net Gain: an update

Biodiversity Net Gain (BNG), where applicable, requires developments in the UK to deliver at least a 10% uplift measured using Defra’s biodiversity metric. Following the first year of implementation, the Government has now published its long-awaited response to the May 2025 consultations, confirming a number of proposed changes.

May 2025 consultation recap

The first consultation considered how the regime was operating for minor, medium and brownfield development following the first year of mandatory implementation. The consultation considered reforming the exemptions, simplifying the small sites metric, providing flexibility to go off-site for minor developments and delivery of compensation on brownfield sites with Open Mosaic Habitat (OMH) – a priority habitat defined by a patchwork of bare ground, sparse vegetation, and varied early-successional plant communities.

Alongside this consultation, the Government also sought responses on the introduction of BNG requirements for Nationally Significant Infrastructure Projects (NSIPs). The consultation proposed a core approach to BNG for all NSIPs to maintain consistency across sectors and reduce complexity for decision makers.

What the consultation responses revealed

The responses to the May 2025 consultations broadly supported the consultations’ aims, but they highlighted several areas where further consideration or refinement was necessary to ensure fair operation of the regime.

A main concern outlined in the responses was the importance of ensuring BNG operates proportionately, particularly in relation to smaller developments. Respondents generally supported the idea that exemptions thresholds for minor developments need to be clearer and more consistent to avoid disproportionate burdens. Responses also suggested the need for exemptions to be more clearly defined in order to avoid them being applied too widely and avoid the risk of BNG objectives being undermined.

Many responded positively to the suggestion of updating the definition of OMH, to which the Government has confirmed that it will be working to review and improve the existing BNG metric information to assist with clearer identification of OMH and other urban habitats. The responses highlighted that delivering BNG on brownfield land can be more complex and proportionately more costly.

The responses to the BNG consultation for NSIPs were positive with a strong support for maintaining BNG, but respondents felt there is a need for a BNG framework that is ambitious and that we should be aiming higher than 10%, especially for major infrastructure projects.

What the Government confirmed following the 2025 consultations

The responses confirmed the following.

BNG will apply to NSIPs from November 2026. The introduction of the consistent approach to BNG for NSIPs creates equal footing and reduces complexity.

Exemptions
1. All development up to 0.2 hectares (regardless of the type of the development) will be exempt but this does not apply where on-site priority habitats are impacted
2. Regarding the proposed removal of the exemption for a single dwelling house on a site of 0.1 hectares, the Government felt that this will be covered by the new 0.2 hectare based exemption
3. The ‘de minimis’ exemption will continue to be applied but it will be considered alongside the future government response to consultation on BNG for residential brownfield development
4. There will be new targeted exemptions which include:
– Development whose primary objective is to conserve or enhance biodiversity
– Temporary planning permission (for genuinely and wholly temporary development) with a maximum of 5 years
– Development enhancing parks, playing fields and public gardens.

Metric process
1. The calculation/assessment will move to an Excel-based tool to streamline the operation
2. Most proposed Small Sites Metric revisions will not proceed, particularly in light of the 0.2 hectare area-based exemption
3. Private gardens will not be counted for BNG.
4. Further considerations will go to simplifying river condition assessments.

Increasing flexibility to go off-site for minor development
1. The hierarchy will be amended for minor development so that offsite biodiversity gains are given the same preference as onsite habitat creation or enhancement
2. Statutory biodiversity credits will remain a last resort option in the hierarchy
3. Spatial risk will be assessed on Local Nature Recovery Strategy (LNRS) areas only rather than local planning authority and National Character Area boundaries as is currently the case. This will increase flexibility for off-site BNG. This change will apply to all types of developments.

Brownfield development with OMH
1. The metric definition and guidance will be updated to improve identification of OMH and other urban habitats
2. Changes are proposed to allow comparable habitat mosaics to compensate for OMH where they have similar ecological benefits.

A further consultation on targeted exemptions for residential brownfield development is underway. The new consultation on targeted exemptions for brownfield development represents the next step in whether adjustments are needed to ensure BNG operates proportionately alongside brownfield development.

Transitional arrangements

The following are expected to come into force before 31 July 2026:
• The new 0.2 hectare area based exemption
• Removal of the self and custom build exemption
• Temporary planning permission exemption
• Amending the biodiversity gain hierarchy.

Later in 2026, following the responses to the consultation on BNG brownfield exemptions, Defra expects to bring forward secondary legislation to exempt those whose primary objective is to conserve biodiversity and targeted developments that enhance parks, playing fields and public gardens.

Pending the outcome of the BNG brownfield exemptions consultation, this secondary legislation may also include changes to the de minimis threshold and the introduction of targeted exemptions for brownfield development.

In the meantime, the existing legislation, regulations and guidelines must be complied with.

What this means in practice

For developers
The changes set out by the Government are intended to reduce disproportionate costs and unnecessary complexity for smaller developments. The new 0.2 hectare exemption aims to “reduce administrative burdens and improve flexibility for minor developments”. The exemption will remove a significant amount of smaller schemes from the scope of mandatory BNG, which reduces cost and programme risk for small sites.

The confirmed changes to the BNG hierarchy should allow flexibility to deliver BNG off-site, helping to reduce design constraints and lengthy negotiations.

BNG is still a core requirement for larger developments, particularly where OMH may be present. Developers bringing forward residential schemes on previously developed land should also monitor the outcome of the new targeted exemption consultation for brownfield development sites, as further exemptions may be introduced.

For local authorities
The 0.2 hectare exemption will benefit local authority capacity, allowing them to focus resources on bigger schemes. Local authorities will need to pay close attention to the guidance on the exemption framework and ensure any policies and guidance are updated accordingly.

Infrastructure promoters
The delayed introduction date for BNG for NSIPs is to allow for developers to have enough preparation time to incorporate the new framework into their procedures. Some of the changes do ease the requirements for NSIPs, such as the streamlined framework only applying to those habitats which are impacted by the development and reduces the application to temporary habitats. Promoters will need to ensure that BNG is embedded within their development consent orders to ensure their projects align with their BNG requirements.

To landowners and habitat providers
The Government’s continued support for the off-site market for nature is likely to expand demand for landowner-provided habitat units. The new frameworks will provide clearer expectations for habitat creation and monitoring which will benefit those landowners in maintaining and producing habitats. This is a clear signal that the Government is backing the ever-growing natural capital market.

Concluding thoughts

Whilst BNG is still in a state of flux, with more changes on the horizon and many players still finding their feet, progress is being made on the ways in which the ideology behind the regime can be advanced, with the emphasis being on simplification and future-proofing.

Not directly mentioned in the Government’s responses, natural capital investment is an important part of ensuring that BNG provision is maintained and improved over the decades to come. But equally as important is the ability not to lose focus of the core principles of recovery and gain, i.e. increasing biodiversity (natural habitats) across the UK. There will always be a struggle between the Government’s goal to provide housing for the millions whilst at the same time increasing natural habitats.

Strong opposition to the additional exemptions is being aired, with the accusation that BNG is being diluted and the rules weakened, resulting in the potential devastation of local (small-scale) nature, damaging community well-being, and the destruction of wildflower meadows, wetlands and woodlands on and around sites which are under 0.2ha. Government must respond sensitively in order to maintain public confidence.

Some of the BNG regulations relating to NSIPs came into force on 7 May 2026 (SI 2026/492) ahead of the implementation date of 2 November 2026. These are amendments to the Planning Act 2008 by Section 99 and Schedule 15 of the Environment Act 2021, which include modifications to Section 103 to 105 and the insertion of Schedule 2A to the 2008 Act. They incorporate provisions that set out the specifics necessary for a biodiversity gain statement and objective and the approaches to developments already covered or not covered by an existing policy statement, specifically preventing the Secretary of State from granting a DCO for a NSIP unless they are satisfied that the biodiversity gain contained in the statement is met. Other regulations (SI 2026/494) come into force on 29 May 2026, which make small targeted amendments to The Biodiversity Gain Site Register Regulations 2024 in relation to NSIPs.

For advice on your BNG questions and any other related issues with our specialist planning and development lawyers, please contact a member of the team.