Biodiversity net gain in England

[edit] Introduction

Biodiversity net gain (BNG) is a planning requirement introduced under the Environment Act 2021 that requires new developments in England to deliver a measurable improvement in biodiversity compared to the pre-development baseline. From February 2024, a minimum 10% biodiversity net gain became mandatory for most major developments in England.

[edit] Legislative background

Schedule 14 of the Environment Act 2021 introduced mandatory BNG requirements in England. The requirement was phased in as follows:

• February 2024: Mandatory for major developments (10 or more dwellings, or over 0.5 hectares)
• April 2024: Extended to small sites (under 10 dwellings)
• April 2024: Extended to nationally significant infrastructure projects (NSIPs) under a separate regime

Prior to mandatory BNG, many LPAs in England included BNG requirements in local plans on a discretionary basis.

[edit] The 10% BNG requirement

Developers must demonstrate that their scheme will deliver at least 10% more biodiversity value after development than was present on the site before. This net gain must be maintained for a minimum of 30 years.

The requirement applies to the habitat units and hedgerow units present on the development site. A 10% net gain must be achieved across both habitat and hedgerow metrics independently.

[edit] How biodiversity is measured

Biodiversity is quantified using the statutory biodiversity metric developed by Natural England (Metric 4.0 as of 2024). The metric calculates biodiversity units based on:

• Habitat type
• Habitat condition (assessed as Poor, Moderate, or Good)
• Spatial risk multiplier (accounting for geographic risk to habitat creation)
• Temporal risk multiplier (accounting for the time required for habitat to reach its target condition)

Assessments must be carried out by a suitably qualified ecologist. The metric is publicly available as a downloadable Excel tool from Natural England.

[edit] Delivering BNG

Biodiversity net gain can be delivered through three routes, applied in order of preference (the mitigation hierarchy):

1. On-site habitat creation or enhancement: The preferred route. Habitat is created or improved within the development site boundary.
2. Off-site habitat creation or enhancement: Where on-site delivery is not possible or sufficient, developers can create or enhance habitat on land outside the development site. This land must be secured through a Section 106 agreement or conservation covenant.
3. Statutory biodiversity credits: As a last resort, developers can purchase statutory biodiversity credits from the government. Credits are priced to incentivise on-site and off-site delivery.

BNG habitats must be secured and managed for a minimum of 30 years through a legal agreement.

[edit] BNG and the planning condition discharge process

In most cases, BNG is secured through a combination of planning conditions and legal obligations. Pre-commencement conditions typically require submission and approval of:

• A pre-development biodiversity metric calculation
• A biodiversity gain plan detailing how the 10% net gain will be achieved
• A habitat management and monitoring plan (HMMP)

Post-development, a post-completion metric calculation and monitoring reports are usually required to demonstrate that the committed habitat units have been delivered.

[edit] Exemptions

The following development types are exempt from mandatory BNG requirements:

• Householder applications (extensions, loft conversions etc.)
• Development with a de minimis impact on biodiversity (no impact on priority habitats and less than 25 square metres of impact on non-priority habitat)
• Permitted development (unless a condition is imposed requiring BNG)
• Biodiversity gain sites themselves
• Development subject to a hybrid BNG approach under the NSIP regime
• Self-build and custom-build housing (fewer than 10 units)