Biodiversity Net Gain reform; CIAT briefing

1 CIAT BNG reform briefing
2 Reforming BNG for minor, medium and brownfield development (CIAT briefing, May 2026)
3 Related articles on Designing Buildings

[edit] CIAT BNG reform briefing

CIAT has prepared a short briefing outlining the government's plans for reform of biodiversity net gain requirements for minor, medium and brownfield developments in England.

In May 2025, the government launched a consultation on improving the implementation of biodiversity net gain (BNG) for minor, medium and brownfield development in England. In April 2026, the government published the outcome of that consultation, outlining next steps for BNG reform.

This briefing summarises the government's plans, to help CIAT members and affiliates understand how BNG requirements may change for their projects. The full consultation outcomes can be found here.

A PDF copy of this briefing can be found here see alo article Biodiversity Net Gain; origins, updates and terminology.

[edit] Reforming BNG for minor, medium and brownfield development (CIAT briefing, May 2026)

This briefing outlines the government’s plans for reform of biodiversity net gain requirements for minor, medium and brownfield developments in England

[edit] Background

1. In May 2025, the government launched a consultation on improving the implementation of biodiversity net gain (BNG) for minor, medium and brownfield development in England. The details of that consultation can be found here: https://consult.defra.gov.uk/defra-biodiversity-net-gain/improving-the-implementation-of-biodiversity-net-g/

2. In April 2026, the government published the outcome of that consultation, outlining next steps for BNG reform. This briefing summarises the government’s plans, to help CIAT members and affiliates understand how BNG requirements may change for their projects. The full consultation outcomes can be found here: https://www.gov.uk/government/consultations/improving-the-implementation-of-biodiversity-net-gain-for-minor-medium-and-brownfield-development/outcome/government-response-and-summary-of-responses#introduction-and-context

[edit] Improving exemptions

3. A key focus of the consultation was on improving and streamlining current exemptions to ensure that BNG delivers its core objective of enhancing biodiversity, without placing an undue burden on small developments.

4. Having consulted on a blanket exemption for all developments up to 0.1 hectares in size, government has confirmed that it will instead implement an exemption to BNG requirements for all developments of 0.2 hectares or less (based on the red line boundary of the site). This will not apply where onsite priority habitats are impacted.

5. The 0.2-hectare threshold was trailed in December, and is expected to mean around 50% of residential planning applications in England (or around 18,900 dwellings annually) are exempt from BNG. Government estimates this will result in only a 12% reduction in compensated biodiversity units, with the focus shifting towards larger, more impactful projects. While CIAT supports BNG as a key element of broader nature recovery, the Institute believes it is sensible to exempt the smallest developments, where implementing BNG can be disproportionately burdensome for developers and local authorities, while bringing comparatively limited benefits, and therefore supports this change.

6. The introduction of the 0.2-hectare exemption is expected to cover the vast majority of projects which currently utilise the small-scale self-build and custom build development exemption. Therefore, that exemption will be removed to streamline the wider BNG framework. Additionally, government will not implement a blanket exemption for all minor developments (i.e., developments up to 9 dwellings and 1 hectare in size).

[edit] 7. New exemptions will be implemented for:

development whose primary objective is to conserve or enhance biodiversity (where BNG is superfluous, and may make it harder to deliver wider biodiversity aims)
temporary planning permissions covering permissions granted for a maximum of 5 years (where the scope for onside BNG is limited, as land must be restored to its previous condition)
development enhancing parks, playing fields and public gardens (where very large site boundaries or high value habitats withing the boundary would make BNG requirements overly burdensome).

8. A key discussion point in responses to the consultation was the current de minimis exemption, which currently exempts all developments which do not impact priority habitats and impact less than 25 square metres (5m by 5m) of onsite area habitat, such as grassland, and 5 metres of onsite linear habitats, such as hedgerows. The consultation proposed increasing the de minimis exemption, however there were widespread concerns that this would open up the system to abuse (with emerging evidence that the exemption is being over-used even at the current threshold). CIAT therefore did not support a change, taking the view that a simple site area exemption is more appropriate and more easily enforceable.

9. For the time being, government has opted to maintain the current de minimis exemption, taking the view that low impact applications on larger sites, such as change of use applications, installation of solar panels on industrial buildings or upwards extension of large blocks of flats should remain exempt. However, government will consider the exact threshold further, pending the outcome of an ongoing consultation on BNG for residential brownfield development, and may move to strengthen enforcement.

[edit] Streamlining the BNG metrics process

10. Following the consultation, government intends to make several changes to make the metrics process easier to use, including:

Moving to a digital, integrated service from the current excel-based tool.
Considering options to streamline benchmarking when using the Small Sites Metric (SSM) including making better use of existing mapping data or image analysis to better support SME developers.
Considering what additional guidance could be provided for small sites development.

11. Government has taken the view that the implementation of the 0.2-hectare exemption will make other proposed changes, such as simplifying habitat types or allowing for the use of the SSM on minor developments which include priority habitats, protected sites or European protected species.

12. Government has also opted not to allowed for biodiverse features in private gardens to be counted towards BNG due to the challenges of monitoring and compliance. However, CIAT still recommends that such features be implemented where possible, as part of the creation of higher quality, more sustainable developments.

13. Government sought views on the proportionality of river condition assessment surveying for minor developments. Under the current model, the sites using the main metric (which includes minor developments which include certain watercourse features), must use river condition assessments, which can be burdensome. CIAT therefore supported reform for minor developments.

14. Government has not reached a conclusion on potential policy changes, but is considering:

whether a simplified condition assessment could reduce costs, lessen burdens, and save time while retaining ecological integrity.
how this would work alongside the existing methodology.
whether adding a new distinctiveness category for heavily modified watercourses could help ease BNG pressures for sites, particularly where achieving ecological improvements on heavily modified or constrained watercourses is challenging.

15. Any changes to metric processes will include transitional arrangements, with a clear timeline for transition between methodologies.

[edit] Off-site BNG

16. A key challenge on smaller sites can be delivering sufficient BNG. CIAT has supported increased flexibility for small sites to meet BNG requirements through off-site delivery, so long as it is within the same local nature recovery area as the site. This would reduce the burden on developers and potentially allow for the creation of more substantial, and higher quality areas of Biodiversity, alongside smaller “stepping stones”.

17. Government has determined that it will amend the BNG hierarchy so that off-site and on-site habitat gain will be afforded the same preference for minor developments (up to 0.5 hectares or 10 dwellings). Other elements of the hierarchy will remain unchanged, including avoiding adverse effects prior to mitigation, with statutory biodiversity credits as the last resort. Broader planning policies, such as that that trees should be retained wherever possible, will not be affected.

18. Government has also confirmed that it will increase flexibility in the spatial risk multiplier, by applying it based on local nature recovery areas, rather than local planning authority areas. As there are 48 of the former, compared to 337 of the latter, this will give greater flexibility in where off-site units can be sourced before the spatial risk multiplier applies. However, the multiplier will remain in place for all development, including minor development.

[edit] Brownfield development with open mosaic habitat

19. Delivering BNG on brownfield sites has often proven costly and expensive, due to the presence of open mosaic habitat, (a priority habitat characterised by a mix of bare ground and vegetated patches (including flower rich meadows, grasslands, scrub) with potential for wet areas). OHM can be hard to correctly identify and may be expensive to secure offsite.

20. Government has committed to working with industry to improve the existing biodiversity net gain metric information to assist with clearer identification of OMH and other urban habitats. Additionally, government will explore allowing for alternative mosaic habitat units to be used to compensate for lost open mosaic habitats.

21. Government is moving forward with a consultation on BNG on brownfield sites, including the potential for exempting such sites up to a maximum threshold of 2.5 hectares, though at present, brownfield remains within-scope for BNG.

[edit] Next steps

22. Government aims to bring forward regulation before the summer to:

introduce the new 0.2-hectare area based exemption
remove the self and custom build exemption
exempt temporary planning permissions granted for a maximum of 5 years
amend the biodiversity gain hierarchy for minor development only

23. The intention is that these changes will come into force before 31 July 2026 (parliamentary time allowing). Further regulatory and process changes will be brought forward thorough late 2026 (and likely into 2027). No timeline has been confirmed for digitising metric tools.

24. Government is currently consulting on further reforms to BNG for brownfield sites (closing 10 June). CIAT intends to respond to this consultation, and members and affiliates are encouraged to contribute feedback to that consultation by email to externalaffairs@ciat.global before 31 May 2026.