Is the UK Government About to Undermine a Cornerstone of Its Post-Brexit Environmental Framework?

As environmental lawyers, planners, and sustainability professionals reflect on the direction of environmental governance in the UK, one issue stands out this summer: the proposed rollback of Biodiversity Net Gain (BNG) requirements for small-scale developments in England.

Reports suggest the government may seek to exempt residential and commercial developments under 1 hectare from mandatory BNG obligations.  At first glance, this may appear to be a narrow planning reform.  In reality, it raises fundamental questions about the coherence, legality,and credibility of the UK’s post-Brexit environmental regime.

What Does the Law Require?

The Environment Act 2021, a flagship piece of legislation, introduced a statutory requirement for most new developments in England to deliver at least 10% biodiversity net gain.  This gain must be:

• Measured using the Defra biodiversity metric;
• Demonstrated pre-application and secured as a planning condition or obligation;
• Maintained for a minimum of 30 years;
• Delivered either on-site, off-site, or through the emerging biodiversity credits market.

This statutory mechanism—largely operational since February 2024—was designed to ensure that development could proceed in tandem with ecological enhancement.  It also provided a long-awaited replacement for EU environmental safeguards lost through Brexit.

What’s at Stake?

According to analysis by Friends of the Earth and planning consultancies, the proposed exemption for sub-1-hectare sites could affect over 97% of planning applications in England and, if implemented, would:

• Remove the requirement for biodiversity gain from the overwhelming majority of housing developments;
• Significantly reduce the cumulative effectiveness of the BNG regime;
• Potentially create perverse incentives to segment development sites below the 1 ha threshold;
• Undermine the emerging private market for biodiversity units and habitat banking, which depends on broad demand.

Legal Concerns

Several legal risks, with the potential to give rise to legal challenges, are likely to arise if this exemption proceeds:

1. Statutory Conflict with the Environment Act 2021

The Act does permit certain exemptions, but blanket removal of the statutory duty to ensure a 10% BNG net gain for a vast majority of developments could be viewed as contrary to the object and purpose of the legislation.  If implemented via secondary legislation or policy guidance (e.g. National Planning Policy Framework revision) rather than primary legislation, it may face a challenge for being ultra vires.

2. Strategic Environmental Assessment (SEA) and Environmental Impact Assessment (EIA)

Policy changes with significant cumulative environmental effects must be subject to SEA under the Environmental Assessment of Plans and Programmes Regulations 2004.  Exempting 97% of development sites from a core ecological duty arguably triggers the need for SEA.  A failure to conduct cumulative or strategic environmental impact assessments would give rise to potential administrative law challenges and could render the exemption unlawful.

3. Habitats Regulations Compliance

Where small-scale developments occur near European protected sites (e.g. Special Areas of Conservation, Special Protection Areas), the lack of BNG may result in unmitigated impacts.  The government remains bound by the Conservation of Habitats and Species Regulations 2017(as retained EU law), requiring appropriate assessments for plans likely to have a significant effect.

4. Public Law and Procedural Fairness

If the proposed change is made without formal consultation, it may breach principles of procedural fairness, irrationality, or legitimate expectation.  Local Planning Authorities, developers, landowners, and ecological consultants have made significant investments in aligning with the current regime.  Abrupt deregulation may be open to judicial review.

There may well also be potential challenges brought in relation to breaches of the UK’s international obligations under UK treaty commitments on biodiversity.

Broader Policy Implications

This policy shift also has wider ramifications for:

• The UK’s international credibility ahead of hosting COP16 of the Convention on Biological Diversity;
• The delivery of the 25-Year Environment Plan, where net gain is central to “leaving the environment in a better state”;
• Investor and developer confidence in natural capital markets, habitat banks, and offset registries.

In short, the rollback risks eroding trust in environmental law as a stable framework for sustainable development.

Final Thought

Environmental regulation must evolve – but it must do so with evidence, transparency, and legal integrity.  Biodiversity Net Gain is not red tape; it is a legal tool designed to reconcile growth with nature recovery.  Diluting it without robust safeguards would be a step backward – legally, ecologically, and politically.

Now is the time for due process, public scrutiny, and principled decision-making.

Should environmental duties be lightened in the name of housing delivery, or is this a false trade-off?