Biodiversity Net Gain (BNG) is policy where new development must deliver measurable improvements for nature by creating or enhancing wildlife habitats. The approach was introduced through the Environment Act (2021), and came into force in February 2024.  

It requires developers to provide a minimum 10% increase in biodiversity from their developments, in comparison to the pre-construction condition of the site. In practice, this means that new developments must leave nature in a better state than they found it, fostering a positive relationship between development and nature’s recovery. 

This requirement for a minimum net gain is calculated using the Biodiversity Metric, which measures biodiversity value across a range of habitats, including grassland, hedgerows, woodland and watercourses. The formula takes account of habitat size, condition, strategic significance and type. The habitat gain can be delivered on-site, off-site or via government biodiversity credits.  

To meet the legal target in the Environment Act to halt nature’s decline by 2030, it is essential that new developments meet BNG requirements. However, a critical issue with the policy is emerging. 

Currently, BNG exemptions are at risk of abuse.  According to research cited by the Green Finance Institute, as little as 0.5% of total planning applications submitted since BNG came into force in February, may have delivered net gain. A shockingly low number for a policy that is supposed to be largely universal across new development.  

Commonly abused exemptions consist of: 

The de minimis exemption (a ‘minimum size threshold’) which exempts developments below a minimum level of habitat loss. This applies to developments that impact less than 25 square metres of non-priority, onsite habitat.  

This exemption has opened a loophole, which allows developers to carefully locate built footprints, with a view to argue that less than 25 square metres of habitat is directly impacted. This means that habitats can be fragmented and polluted by carefully placed developments, having detrimental impacts on nature while not qualifying for BNG measures.  

In addition, the self and custom build exemption which exempts self-declared, self and custom build developments [consisting of nine dwellings or less] on sites of 0.5 hectares or less, also represents a critical risk.  

Abuse of these exemptions is further enabled by resource-strapped planning departments lacking ecological expertise, making it difficult to assess claims about the relationships between individual buildings and the surrounding habitat. It can also be difficult to verify when a development is genuinely a self-build.  

As we know, nature does not register whether a damaging development is self-built or not; unmitigated damage is unmitigated damage. 

We need urgent policy action 

These abuses of exemptions are detrimental to our wildlife and the valuable habitats which they call home. If the Government is to successfully achieve its joint aims to deliver new housing and support nature’s recovery, these loopholes in BNG policy must be urgently addressed. We call on the Government to: 

• Immediately instigate a review of The Biodiversity Gain Requirements (Exemptions) Regulations 2024, with a view to amending the Environment Act 2021, to reduce de minimis to sites with a total area of 5 metres squared or less, or 5 square metres of direct impact, and remove the self and custom build exemption. 

• Disincentivise use of the de minimis loopholes by introducing stringent evidence requirements to planning applications invoking the exemption. The Comprehensive Spending Review 2024 should dedicate funds for increasing enforcement and ecological capacity in local authorities, to uphold this through better monitoring and enforcement of delivery of BNG commitments. 

Without taking these steps, the Government’s pledge to deliver new development that helps nature recover, through biodiversity net gain, risks being a ‘net that’s full of holes’, with our wildlife being the ultimate loser.