Is the implementation of biodiversity net gain for minor, medium and brownfield development changing?

This update explores the key takeaways from the Government’s response to the consultation  on improving the implementation of biodiversity net gain for minor, medium and brownfield development.

In May 2025, Defra launched an eight-week consultation on improving the implementation of biodiversity net gain (BNG) for minor, medium and brownfield development (the “Consultation”). The consultation explored four key areas: improving exemptions, streamlining the BNG metric process, increasing flexibility to go off-site for minor development and dealing with brownfield development with open mosaic habitat (OMH).

On 15 April 2026, Defra published its response to the consultation, confirming a package of changes intended to reduce cost and delay for smaller schemes, whilst retaining protections for priority habitats. We have set out a summary of the key takeaways below followed by further details on the changes.

What are the key takeaways?

• New 0.2 ha exemption: Defra confirms an area-based exemption for development where the site area is 0.2 hectares or below, subject to a carve-out where priority habitats are affected.
• Reform of existing exemptions: Defra’s response also signals reforms and clarifications to the existing exemptions framework (including how exemptions are evidenced and applied in practice), alongside the new area-based threshold.
  • The exemption for small-scale self-build and custom build development is expected to be removed.
  • ‘De minimis’ exemptions will be considered alongside the future government response to the consultation on BNG for residential brownfield development. 
• New exemptions will be introduced for the following types of development:
  • development whose primary objective is to conserve or enhance biodiversity;
  • temporary planning permissions covering permissions granted for a maximum of 5 years; and
  • development enhancing parks, playing fields and public gardens.
• Minor development hierarchy: Defra indicates it will amend the biodiversity gain hierarchy for minor development to provide more flexibility on constrained sites.
• Brownfield remains in scope: No blanket exemption has been introduced for brownfield; however, Defra has opened a further consultation on 15 April 2026 on a targeted exemption for residential brownfield development. Defra has confirmed that it will work to improve the existing BNG regime for brownfield development with open mosaic habitat.

What is changing?

The new 0.2 hectare exemption

Following the Consultation, the Government agreed that an area-based exemption would provide a simplified approach to exemptions that will ease burdens on small developers and local planning authorities. As a result, Defra has confirmed it intends to exempt development where the site area is 0.2 hectares or below from the mandatory 10% BNG requirement. The exemption is framed as a practical, objective threshold intended to reduce disproportionate cost, delay and uncertainty for the smallest schemes.

The exemption is not intended to apply where onsite priority habitats would be affected. Further detail, including any other conditions, will be specified in secondary legislation.

New targeted exemptions

Defra has confirmed it will use secondary legislation to introduce a small set of further, targeted exemptions. While the detailed drafting and specifics of any conditions are still to be confirmed, the policy intent is to remove BNG requirements where development is inherently biodiversity-positive, time-limited, or focused on improving public green space. These include:

• A new exemption for a development whose primary objective is to conserve or enhance biodiversity, intended to avoid applying BNG where the scheme is inherently biodiversity-positive, for example habitat creation or restoration projects).
• A new exemption for temporary development which is for 5 years or less, recognising that short-lived or reversible development can make long-term BNG delivery disproportionate.
• Targeted exemption for development that enhances parks, public gardens and playing fields, where the development is not already exempt, including by the new 0.2 hectare area-based exemption,  and where no onsite priority habitats are impacted.

Reform of existing exemptions

Defra’s response indicates that the existing exemptions framework will be updated as follows:

• The exemption for small-scale self-build and custom build development is expected to be removed. Defra expects that small-scale single dwellings will be covered by the new 0.2 hectare area-based exemption.
• ‘De minimis’ exemptions will be considered alongside the future government response to the consultation on BNG for residential brownfield development.

Brownfield land

Although no exemption has been introduced for brownfield land, a further consultation on a targeted exemption for residential brownfield development has been opened. This follows feedback from a number of respondents who highlighted that delivering BNG on brownfield land can be more complex and proportionately more costly than on other sites. The new consultation will explore appropriate definitions of brownfield land and consider a range of potential exemption thresholds, up to 2.5 hectares, and is open until 10 June 2026.

Streamlining BNG for minor and medium development

The consultation also asked how the statutory metric and supporting process could work more proportionately for minor and medium schemes. Defra’s response indicates further work to simplify and streamline the BNG assessment process for smaller sites with the aim of reducing cost and delay without weakening outcomes for priority habitats.

Defra confirmed that they are not intending to make the majority of proposed revisions to the small sites metric (“SSM”) at this time. The introduction of the new area-based exemption for sites of less than 0.2 hectares is expected to remove more than 50% of the smallest planning applications which are currently delivering mandatory BNG from the BNG requirement. Many of the challenges cited in the consultation around use of the SSM were raised by the smallest developers, who will be exempt under this threshold. Defra has, however, confirmed that it will be taking forward the development of a web-based metric tool and, as part of this, will consider how best to support small- and medium-sized developers within the future metric service.

Defra has confirmed that regulations will amend the BNG hierarchy for minor development only (defined as not major development), where it is not already exempt. Off-site biodiversity gains will be treated as equally preferable to on-site enhancement/creation for minor development (i.e., off-site moved up the hierarchy for this category).

Defra has confirmed that they will change how spatial risk is assessed. This will include assessing spatial risk based on local nature recovery strategy (LNRS) areas only, rather than local planning authority (LPA) and National Character Area boundaries as is currently the case. The changes will apply to all development types, not just minor. As a result, developers can source off-site units across a larger “local” area without the multiplier applying, improving flexibility and aligning with future local government reorganisation.

Brownfield development with open mosaic habitat (OMH)

Defra has confirmed that it will review and improve the existing biodiversity net gain metric information to support clearer identification of OMH and other urban habitats given the additional complexity and cost involved in assessing OMH habitats. This may include the following:

• Review and improve metric information so OMH/urban habitats are identified more clearly.
• Review urban condition sheets and explore a new medium distinctiveness habitat type to better capture derelict/abandoned land habitats that aren’t OMH but don’t fit current metric categories well.
• Enable use of proxy habitats (alternative habitat mosaics with similar ecological benefits) where OMH units can’t be sourced.

How will the reforms be implemented?

The reforms are expected to be delivered via secondary legislation. Whilst no date has been confirmed, it is expected that reforms will come into effect at the end of July 2026. Until the new regulations are made and in force, the current statutory BNG regime continues to apply.

What are the next steps?

With the consultation response in mind, developers should seek to:

• Check site area early: if your red line boundary is close to 0.2 hectares, small changes to the boundary could determine whether BNG applies once the exemption is in force.
• Plan for the transition: until the secondary legislation is in force, the current BNG rules apply. For live and imminent applications, timing and any transitional provisions in the final regulations will be critical.
• Track and comment on further consultations: the proposed targeted exemption for residential brownfield development is currently being consulted on, and could be relevant for regeneration pipelines.
• Check when the changes will come into effect: it is expected that these changes will take effect from 31 July 2026 through secondary legislation (subject to Parliamentary scheduling).

We have extensive experience in advising on BNG for TCPA schemes, so please contact Matthew Tucker  or Sofiya Yerokhina if you have any queries.