ISEP responds to Government consultation on BNG for small, medium and brownfield sites

29 July 2025

The pioneering Biodiversity Net Gain (BNG) legislation that was introduced in England in early 2024, mandating a 10% gain for biodiversity in the majority of new developments.

BNG is a world-leading mechanism for conserving and restoring nature and offsetting biodiversity losses across both major and small-scale development, currently excluding Nationally Significant Infrastructure Projects (NSIPs).

The approach puts an onus on developers to quantify any biodiversity losses during construction and compensating for any nature losses by funding an equal amount of habitat restoration plus at least an additional 10% - preferably onsite or at an alternative location.

Despite Biodiversity Net Gain for minor developments and small sites being launched less than 18 months ago, the UK Government has consulted on introducing a new category of ‘medium’ sites, and begun to look at improving BNG on brownfield sites.

The range of proposals in the consultation include:

–> Exempting all minor developments/small sites from BNG.

–> Exempting temporary sites.

–> Partial exemptions for parks, playing fields and gardens.

–> Increasing the de minimis for the site size that triggers the need for BNG.

–> Removing the trading rules from the Defra Small Sites Metric.

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Informed by a workshop of ISEP members and key stakeholders, ISEP noted the following considerations should be taken into account:

–> It’s too short a time after implementation to make major changes.

–> Developers, ecologists, and local authorities are still learning about the implementation of BNG.

–> It is mostly the smallest of the minor developments/small sites that are struggling to meet BNG.

–> The consultation seems to be more about making the process of BNG easier than finding solutions for negative impacts on nature.

–> The removal of BNG for minor developments/small sites will have a significant impact on the availability of biodiversity units.

There has been a groundswell of disapproval across relevant stakeholders to this consultation and we wait to see any changes that come as a result. 

ISEP made the following recommendations:

–> The Government do not exempt all minor developments/small sites from BNG.

–> Only small, evidence-based changes are made with regard to how BNG is completed on minor developments/small sites.

–> BNG should have more time to become established before any major changes are made.

–> Mandate the smallest of the minor developments/small sites to undertake an environmental improvement instead of BNG with all other minor development/small sites continuing to undertake BNG of a minimum of 10%.

–> Create more guidance and training on competence to use the Small Sites Metric.

–> Do not create the new category of ‘medium’ sites and continue to use the Statutory Biodiversity Metric (rather than the Small Sites Metric as proposed).

ISEP consultation response to: Improving the implementation of Biodiversity Net Gain for minor, medium and brownfield developments


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Lesley Wilson AISEP

Policy and Engagement Lead

Lesley is Policy and Engagement Lead at ISEP with a focus on the rapidly developing area of biodiversity and natural capital. On behalf of ISEP, Lesley also supports and is a member of the Steering Group of the UK Business and Biodiversity Forum. Lesley has worked in environmental sustainability for 15 years and previously delivered programmes and solutions in sustainability for business at the British Standards Institution, including ground breaking standards in biodiversity net gain and natural capital. Lesley has a qualifications in business management (MBA) and climate change management, and mentors environmental students at the University of Westminster.