BNG and the Law: Understanding Biodiversity Net Gain Legislation

Biodiversity Net Gain (BNG) is no longer a voluntary initiative—it’s now a legal requirement for most developments in England. As of 2024, understanding the legal underpinnings of BNG is essential for developers, landowners, planning consultants, and ecological professionals alike. In this guide, we’ll walk you through the legal frameworks, planning policy, compliance obligations, and how The BNG Guy can help you stay on the right side of the law.

What is Biodiversity Net Gain (BNG)?

BNG is a planning principle that aims to leave the natural environment in a measurably better state than before development. It requires developers to demonstrate that their projects deliver a minimum 10% net gain in biodiversity value, sustained for at least 30 years.

This isn’t just best practice anymore—it’s enshrined in law under the Environment Act 2021.

BNG and the Law: The Legal Backbone

The statutory requirement for BNG comes from the Environment Act 2021, which received Royal Assent in November 2021. This transformative legislation places biodiversity on the same footing as other key development considerations like highways and flood risk.

The Environment Act 2021

The key legal highlights include:

A mandatory BNG requirement of 10% for most developments in England.
BNG must be secured for at least 30 years, through legal agreements or conservation covenants.
BNG will apply to new planning applications under the Town and Country Planning Act 1990, unless exempt.
All BNG calculations must be conducted using the Biodiversity Metric developed by Natural England.

Section 98 of the Environment Act

Section 98 amends the Town and Country Planning Act 1990 by inserting Schedule 7A, which introduces the BNG requirement. This schedule mandates that a development may not proceed unless a Biodiversity Gain Plan (BGP) is approved by the local planning authority.

When Did BNG Become Law?

The mandatory BNG requirement came into force in stages:

January 2024: Large-scale developments (major applications) must comply with BNG requirements.
April 2024: Small-scale developments also fall under BNG rules.
Late 2025 (expected): Nationally Significant Infrastructure Projects (NSIPs) will be required to comply.

Key Legal Requirements for Developers

Under the law, developers must meet the following criteria:

Submit a Biodiversity Gain Plan for approval before development begins.
Demonstrate a 10% biodiversity uplift using Natural England’s approved metric.
Maintain and monitor habitat gains for at least 30 years.
Secure the BNG delivery legally via a Section 106 Agreement or a Conservation Covenant.

Failure to comply may result in planning refusals, enforcement action, or inability to discharge planning conditions.

Planning Obligations: Section 106 and Conservation Covenants

Section 106 Agreements

These are legal agreements made between a developer and the local planning authority. They are commonly used to secure on-site or off-site biodiversity enhancements.

Conservation Covenants

Introduced under the Environment Act, these are voluntary, private agreements between landowners and responsible bodies (e.g., Wildlife Trusts). They bind the land to biodiversity obligations for 30 years or more and are registered on the title deed.

BNG Metrics and Legally Binding Calculation Tools

BNG must be measured using one of two official tools:

Biodiversity Metric 4.0: For major and complex developments.
Small Sites Metric: A simplified version for smaller developments (fewer than 10 dwellings).

These tools calculate biodiversity units based on habitat type, condition, and strategic significance. They form the evidence base for your Biodiversity Gain Plan.

Exemptions from BNG

Some developments are exempt from mandatory BNG, including:

Householder applications (e.g., extensions, loft conversions).
Change-of-use developments that do not impact habitats.
Permitted Development under the General Permitted Development Order (GPDO).
Urgent Crown infrastructure projects.

However, exemptions do not mean BNG can be ignored entirely. Local planning authorities may still request biodiversity information under their local policies.

BNG in Local Planning Policy

While national law governs the baseline, local planning authorities (LPAs) can implement more ambitious BNG requirements. For example:

London Plan: Encourages urban greening and biodiversity.
Greater Manchester Combined Authority: Aims for 20% BNG in strategic developments.
Oxfordshire and West Midlands: Have adopted habitat banking schemes to facilitate off-site BNG.

Enforcement and Compliance

BNG conditions are now enforceable in the same way as any other planning condition. If the biodiversity uplift is not delivered:

The planning authority can take enforcement action.
You may be required to submit a revised Biodiversity Gain Plan.
Fines or legal proceedings may follow for severe breaches.

How The BNG Guy Supports Legal Compliance

We specialise in simplifying BNG compliance while ensuring full legal adherence. Our services include:

Baseline habitat assessments using Biodiversity Metric 4.0 or Small Sites Metric.
Drafting compliant Biodiversity Gain Plans.
Liaising with LPAs and responsible bodies on Section 106 or conservation covenants.
Arranging off-site BNG units from trusted providers.
Monitoring and reporting strategies for 30-year biodiversity maintenance.

Frequently Asked Questions

Is BNG legally required for all developments?

Almost all new developments must comply with BNG, with some minor exemptions. Check with your planning authority for site-specific advice.

What is the penalty for not complying with BNG?

You risk planning refusals, delays, or enforcement action. Legal obligations are tied to planning conditions and cannot be ignored.

Can I deliver BNG off-site?

Yes, but you must demonstrate that on-site BNG isn’t viable and that off-site delivery achieves the same or better biodiversity value.

How long must BNG habitats be maintained?

Under the law, biodiversity gains must be maintained for a minimum of 30 years.

Conclusion: BNG and the Law is Here to Stay

BNG isn’t a box-ticking exercise—it’s a legal obligation backed by primary legislation and enforceable through planning law. As a developer or landowner, understanding your obligations is critical to avoiding delays and maintaining compliance.

Whether you’re working on a small housing scheme or a large infrastructure project, The BNG Guy is here to ensure you comply with the law while contributing to a greener future.

From first survey to final sign-off, The BNG Guy takes the complexity out of BNG compliance. We handle the science, the paperwork, and the strategy — you get planning approval with confidence.