Mandatory biodiversity net gain is expected to apply to English onshore nationally significant infrastructure projects from 2 November 2026, following Defra's response to its NSIP consultation. The framework broadly mirrors the Town and Country Planning Act regime: the same statutory biodiversity metric, the same 10% minimum, the amended gain hierarchy, and the statutory credit backstop — applied through the Development Consent Order process, with a biodiversity gain statement required as part of the application.
One meaningful difference for promoters: there is flexibility on how off-site delivery operates at this scale, with aggregation permitted so that off-site gain can be delivered within any one of the local planning areas affected by the project rather than split proportionally across all of them.
The deadline is not really 2 November
Policy deadlines are the visible constraint. The binding one is biological.
A baseline for the statutory metric is not a desk exercise. It requires a UK Habitat Classification survey with a condition assessment, and the published condition criteria mostly require the sward to be growing and the flora identifiable. In practice that means roughly mid-April to mid-September, and for a landscape-scale linear or area scheme it means weeks of field time, not days.
For a scheme of NSIP scale, a baseline commissioned in October is not a baseline commissioned late. It is a baseline commissioned for next year.
Where the growing season has closed, the options are to survey precautionarily — assuming the lowest defensible condition, which usually inflates the units you have to deliver — or to wait for spring. Both are expensive. The precautionary route costs units; the wait costs programme.
What an NSIP promoter should have in place
- A habitat baseline surveyed in condition. UKHab mapping with condition assessment across the full Order limits, including land taken temporarily for construction, which is routinely forgotten and routinely caught.
- An agreed scope with the Planning Inspectorate. Use the pre-application process to settle the BNG assessment methodology, the survey extent and the treatment of temporary land take before you are committed.
- Modelled delivery scenarios under the amended hierarchy. On-site, off-site and credits, with the aggregation flexibility used deliberately rather than by default.
- A contingency position on off-site units. The habitat uplift required at infrastructure scale is large, the off-site market is thin in places, and statutory credits are priced to be unattractive. Secure early or price the backstop honestly.
- An ecologist with DCO experience leading the gain plan. The examination process rewards evidence that was designed to be examined.
Where this sits alongside everything else
BNG is arriving on top of, not instead of, the existing ecological requirements for a DCO: Habitats Regulations Assessment where a European site is in play, protected species survey and licensing across the Order limits, and the ecology chapter of the Environmental Statement. On a linear scheme those obligations are already multi-season. Adding a condition-assessed habitat baseline is less a new workstream than a new reason the existing one cannot slip.
If you have not started
Talk to an ecologist this month rather than in October. Even where the field season has effectively closed for condition assessment, there is useful work that can be done now: constraints mapping, data searches, agreeing methodology with the Inspectorate, scoping the Order limits, and booking survey teams for the opening of next season. The projects that handle this deadline well will be the ones that spent the autumn preparing rather than waiting.
Written by the Virtus Green technical team. This is a summary of our reading of current guidance and regulation as at 18 August 2026; it is not legal advice, and positions change. Confirm current requirements with your local planning authority before you rely on anything here.