Biodiversity Net Gain (BNG): Statutory Requirements Explained

Legal Basis

• Town and Country Planning Act 1990 – Schedule 7A (inserted by the Environment Act 2021).
• This Schedule makes BNG a mandatory condition of planning permission for most developments in England.
• The condition applies regardless of whether it is explicitly listed on the decision notice — it is automatically imposed by law.

When Does It Apply?

• Major Developments: Requirement came into force 12 February 2024.
• Small Sites (fewer than 10 dwellings, or <0.5 ha non-residential): Requirement applies from April 2026.
• Exemptions: Certain categories are exempt (e.g. householder applications, sites impacting habitats below a de minimis threshold, nationally significant infrastructure projects).

The Statutory Requirement

All planning permissions (where BNG applies) are subject to the condition that:

1. A Biodiversity Gain Plan must be approved by the LPA before development can begin.
2. The Plan must demonstrate at least a 10% net gain in biodiversity value against the site baseline.
3. The gain must be maintained for at least 30 years (secured via conditions, planning obligations, or conservation covenants).

What Must the Biodiversity Gain Plan Include?

A valid Biodiversity Gain Plan (as per Schedule 7A) must set out:

• Pre-development biodiversity value of the onsite habitat (baseline survey, typically using DEFRA’s Biodiversity Metric 4.0 or Small Sites Metric).
• Post-development biodiversity value expected once works are completed.
• Steps taken to minimise adverse impacts on biodiversity.
• How the +10% net gain will be achieved, whether through:
  • Onsite habitat creation or enhancement,
  • Offsite habitat units (secured via legal agreement), or
  • Statutory biodiversity credits (purchased from the Government as a last resort).
• Maintenance and monitoring arrangements for the 30-year period.

Key Points for Planning Consultants & Applicants

• Validation Risk: Applications without proportionate BNG evidence risk delay or refusal.
• LPAs’ Duty: Planning authorities cannot lawfully approve development without securing the statutory BNG condition.
• Small Sites: While mandatory BNG doesn’t bite until April 2026, many LPAs are already requesting proportionate statements in line with emerging policy.
• Best Practice Now: Demonstrating voluntary net gain strengthens planning submissions and reduces the chance of late-stage requests.

Summary

• BNG is law: Schedule 7A of the Town and Country Planning Act 1990 (Environment Act 2021) makes it a statutory condition of planning permission.
• Minimum 10% uplift in biodiversity value must be achieved and sustained for 30 years.
• Applies now to major sites, and from April 2026 to small sites.
• Biodiversity Gain Plan is the vehicle for demonstrating compliance — and must be approved before works begin.

We provide proportionate, planning-ready BNG statements using the DEFRA Small Sites Metric — helping planning consultants and architects meet these legal requirements with minimal delay or risk.