New BNG exemptions come into force amid mounting criticism of evidence base

Changes to the biodiversity net gain (BNG) regime come into effect today, introducing new exemptions for small sites even as government’s own independent advisers have branded the evidence underpinning the changes “not fit for purpose”.

What’s changing from today?

The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 take effect on 6 August, delivering the first tranche of changes flowing from a consultation launched by DEFRA in May 2025. From today:

• A new exemption applies to sites up to 0.2ha in size, provided no onsite priority habitats are impacted. It applies only to planning applications made after 6 August, and does not apply to section 73 applications (amending a planning condition from a previous consent) where the original permission was granted before the change came into force.
• A new temporary development exemption applies where development is wholly temporary, does not affect onsite priority habitat, and is removed with the land reinstated within five years.
• The biodiversity gain hierarchy for minor development is amended so that onsite habitat enhancement and creation sit on an equal footing with registered offsite biodiversity gains, rather than onsite measures being prioritised first.
• The exemption for small-scale self-build and custom-build development is removed, following feedback that it was difficult to implement and enforce.

Defra has announced that further changes are still to come, including an exemption for development whose primary objective is to conserve or enhance biodiversity (this has been proposed in the recent Permitted Development Rights consultation – but only within EDPs), a targeted exemption for development enhancing parks, playing fields and public gardens, and changes to the statutory biodiversity metric.

Independent advisers rate impact assessment “not fit for purpose”

The changes arrive despite a damning assessment from the Regulatory Policy Committee (RPC), the government’s independent scrutiny body, which has given Defra’s impact assessment for the 0.2ha exemption its lowest possible rating.

The RPC found that the assessment fails to build a case for government intervention, and does not explain why the balance between environmental and business impacts has shifted since BNG was introduced. It also criticised the absence of any review or evaluation of the original small sites policy to inform the proposed changes, said the appraisal of options considered was insufficient, and found the assessment of impacts on small and micro businesses inadequate. The monitoring and evaluation plan was rated weak.

CIEEM Chief Executive, Sally Hayns, said:

“Whilst some of the changes to BNG and new exemptions are sensible, some others risk emasculating the policy to the extent that it fails to deliver any meaningful benefits to biodiversity or developers, especially if the potential brownfield exemptions come into play. Many of us have not been persuaded about the evidence basis for some of the decisions around exemptions and it seems that the Regulatory Policy Committee agrees. Their report into the Government’s impact assessment for the BNG changes have given it a red rating – the lowest possible score. Essentially the Government has failed to make a persuasive case for weakening the legislation to the extent it has. Is it too late or can the Government possibly take a step back, have a rethink, consult genuinely with stakeholders and allow us to work together to fix the problems in the BNG process (which most stakeholders acknowledge had lessened considerably by the time the Government completed the consultation process)?”

De minimis exemption remains a concern

CIEEM has also continued to flag the existing ‘de minimis’ exemption as a problem for the credibility of the BNG approach (see here and here). The exemption allows developers to self-assess that their project will have a negligible impact on biodiversity, and so avoid BNG requirements altogether – with no independent check on that judgement.

CIEEM believes this self-assessment route undermines the wider BNG framework, and is calling on government to address it as part of any further reform.

Green Gap findings on brownfield exemption still unaddressed

Today’s changes do not include the more contentious brownfield exemption consulted on earlier in June this year and which remains under consideration by government. CIEEM continues to raise concerns about that proposal, having part-funded research – The Green Gap report – which found that exempting small brownfield sites from BNG would disproportionately affect disadvantaged communities who already have the poorest access to nature.

Government has yet to acknowledge this evidence in its response to the consultation. CIEEM is urging Defra to properly account for the Green Gap findings, and the RPC’s criticism of the evidence base more broadly, before proceeding further with the brownfield exemption.