The Department for Environment, Food & Rural Affairs has issued detailed guidance about biodiversity net gain (BNG) for developers of Nationally Significant Infrastructure Projects (NSIPs) ; BNG became mandatory for NSIPs on 2 November 2026.

NSIP developers who apply for a development consent order (DCO) on or after this date will now need to deliver at least 10% net gain in biodiversity.

The statutory framework for mandatory BNG for NSIPs is introduced by Schedule 15 to the Environment Act 2021, which inserts Schedule 2A into the Planning Act 2008.

In June 2026, Defra published biodiversity gain statements for NSIPs which explain how NSIPs need to calculate, deliver and report on BNG. The gain statements have the same effect as if they were included in the relevant national policy statement (NPS). The gain statements will be incorporated into the relevant NPS when each NPS is next reviewed.

NSIP developers must follow the biodiversity gain statement relevant to their project to receive development consent. This guidance is supplementary to the gain statements and includes further information and best practice.

Developers will need to calculate the biodiversity value of on-site habitats before development - the BNG baseline. The baseline calculation must include the pre-development biodiversity value of any habitats that will be:

• negatively impacted by the development
• used to contribute towards the development’s BNG
• Any expected negative impacts to habitats includes all habitats subject to permanent or temporary:
• loss – for example, permanent loss due to development or temporary loss during construction
• deterioration of habitat condition (based on the biodiversity metric condition assessment) – for example, from shading or disturbance caused by the development

Developers must consider all expected impacts, including those from:

• development
• enabling and site preparation works
• construction activity, including direct habitat clearance, temporary compounds, storage areas and access routes
• associated development included within the DCO application
• expected impacts during the maintenance and operation of the development

For developers who are uncertain about the extent of habitat impacts who do not know the final extent, the baseline must reflect the realistic worst-case extent of habitat loss or deterioration. This means using the maximum design and construction parameters for a NSIP project, rather than a hypothetical or overly precautionary scenario.

Below-ground and above-ground infrastructure

For below-ground infrastructure or construction techniques, the baseline can exclude habitats above the works if the developer is certain they will not be impacted or degraded, for example:

For the use of below-ground horizontal directional drilling, developers may exclude areas of unimpacted habitat above the drilling area.  Any habitats that will be impacted must be included e.g. during access, set up and working around the drilling access points.

For above-ground infrastructure, the baseline can exclude areas of habitat beneath or immediately next to an above-ground structure where the developer is certain they will not be impacted or degraded, for example:

habitats in the order limits beneath overhead electricity lines can be excluded if the developer is sure they will remain unimpacted by the development. Any habitats that will be impacted by site preparation or construction activity, such as habitats around pylons, access routes, or temporary storage areas, must still be included.

An application for a DCO for a Nationally Significant Infrastructure Project needs to include 

• an outline biodiversity gain plan
• draft DCO requirements relevant to BNG

A DCO application will receive consent only if the Secretary of State is satisfied that the developer is able to meet the 10% BNG objective in line with a gain statement.

Click here to access DEFRA’s detailed guidance on Biodiversity Net Gain for developers of Nationally Significant Infrastructure Projects.