What is Biodiversity Net Gain?

Biodiversity Net Gain (BNG) is a new legal requirement in the UK that aims to ensure development leaves the natural environment in a better state than it was before. Introduced under the Environment Act 2021, BNG became mandatory for most new planning applications in England from February 2024.

Under this legislation, developers must assess the biodiversity value of a site before starting any work and demonstrate how they will deliver a net gain of at least 10% in biodiversity. This gain must be maintained for at least 30 years. The biodiversity value is measured using the government’s Biodiversity Metric, which calculates “biodiversity units” based on habitat type, quality, and location.

The goal is to encourage nature-positive development. Developers can meet the requirement through a hierarchy: first, by enhancing biodiversity on-site; second, by creating or improving habitats off-site; and as a last resort, by purchasing statutory biodiversity credits from the government. Local Planning Authorities are responsible for enforcing compliance and ensuring developers’ biodiversity plans are secured through planning conditions or legal agreements.

Some developments, such as small-scale self-builds and certain brownfield sites, may be exempt or subject to transitional arrangements. However, most major and minor developments now need to incorporate BNG into their design and planning from the outset.

BNG represents a significant shift in how planning and environmental conservation intersect in England. It integrates ecological considerations into the heart of development, aiming to reverse biodiversity decline and support the UK’s broader environmental goals. While implementation presents challenges—particularly around costs, land availability, and monitoring—BNG is also seen as a major opportunity to embed nature recovery into everyday planning decisions and land use change.