From 2 November 2026, applications for development consent for nationally significant infrastructure projects in England must deliver a minimum of 10% biodiversity net gain. The requirement comes from Schedule 15 of the Environment Act 2021, which amends the Planning Act 2008, and it applies across every NSIP type. There are no sector carve-outs.
If you work on NSIPs, this is not a distant policy signal. It is a dated change to what a development consent order application has to contain, and the work that supports it starts long before the application does.
This piece sets out what the requirement covers, what has to be submitted, where the practical pressure points sit, and what the November date means for programmes already in flight.
Mandatory biodiversity net gain has applied to most development under the Town and Country Planning Act since 2024. NSIPs were held back, and the date moved more than once. It is now fixed.
The headline points:
The biodiversity gain statements that give this effect were laid in Parliament in May 2026, and the first tranche of guidance was published by Defra on 2 June 2026. Further priority guidance covering gain plans, monitoring and adaptive management has been promised.
Three documents do most of the work.
An outline biodiversity gain plan, submitted at application stage. This is where you set out your baseline, your metric calculation, and how you intend to reach 10%. It is updated after consent, and a final position on any shortfall is settled before operation.
A BNG boundary plan. This is a drawing, and the guidance is specific about it. It must sit over the order limits and distinguish four categories: habitats negatively impacted by the development, habitats contributing to biodiversity gains, unimpacted habitats included in the baseline, and unimpacted habitats excluded from it. It needs a scale, a north arrow and a clear legend.
A draft habitat management and monitoring plan, also at application stage. This is the point that catches people out. A draft HMMP at submission means ecological survey work, habitat design and management planning all have to be sufficiently advanced before the application is made, not after.
You will also need a short statement covering the role and input of the qualified ecological professionals involved, including their credentials and their part in the metric calculations and management planning. Named accountability is now part of the submission.
One feature of the NSIP regime differs from the town and country planning approach, and it matters commercially.
For NSIPs, BNG is required only on habitats impacted by the development, rather than across the whole site. The baseline has to capture two things: every habitat within the order limits facing permanent or temporary loss or a deterioration in condition, and the pre-development value of any habitat where on-site enhancement or creation will happen.
Unimpacted habitat inside the order limits can be excluded, but only where an ecologist confirms there will be no permanent loss, no temporary loss and no deterioration in condition. Areas above confirmed below-ground infrastructure are the usual example.
For a linear scheme running across a long corridor, that distinction can be the difference between assessing everything inside the red line and assessing a fraction of it. It is also a judgement that has to be evidenced. The guidance is clear that the robustness of the ecologist's reasoning will matter for any exclusion, which means you need enough habitat information across the whole order limits to justify what you left out. Excluding land still requires you to have looked at it.
That is a slightly awkward truth: to prove you did not need to assess something, you need some assessment of it.
NSIPs get a concession that other development does not. Habitats of low or very low distinctiveness that are temporarily impacted do not have to be recorded as lost, provided they are restored to their baseline condition within five years. Elsewhere the equivalent window is two years.
For construction corridors, compounds, haul roads and laydown areas, this is significant. It recognises that infrastructure construction runs on a different timescale to a housing scheme.
Two cautions. First, the concession applies to low and very low distinctiveness habitat only. Second, those habitats are still negatively impacted habitats, so they still go into the baseline and still appear on the BNG boundary plan. The concession affects how the loss is scored, not whether the land is assessed.
Most NSIPs go to application with elements of the design still flexible. The guidance addresses this directly: where locations or construction areas are not yet fixed, the baseline should reflect the realistic worst-case extent of habitat loss or deterioration, using maximum design and construction parameters.
Anyone who has worked with a Rochdale envelope will recognise the logic. The practical consequence is that the baseline has to cover more ground than the final scheme will touch, because you are assessing the envelope rather than the outcome.
That expands the survey area, and it expands it at precisely the stage when the design team least wants to commit.
Ancient woodland, and other habitats that would be technically very difficult or take a very long time to restore, recreate or replace, are treated separately.
They are excluded from the baseline and from the 10% obligation. Where they are lost, bespoke compensation is required, it must be secured, and it cannot be counted towards the biodiversity net gain obligation. Statutory credits cannot be used for it either.
The direction of travel is straightforward. Losing irreplaceable habitat is expensive and cannot be offset with units. Identifying it early, at the route or site selection stage rather than at application, is where the value sits.
Three consequences follow from the detail above.
The baseline has to be earlier and wider than it used to be. A draft HMMP at application means the ecology has to be substantially complete at submission. A worst-case envelope means surveying more than the final footprint. An exclusion argument means having enough evidence about land you are not assessing in full.
Survey seasonality becomes a programme risk rather than an ecology detail. Habitat condition assessment is most reliable in the growing season, and protected species surveys have their own windows. A consent programme that needs a baseline in January has a problem that no amount of resourcing solves. We look at that constraint, and the ways teams are working around it, in why the NSIP consent timeline outruns the ecological calendar.
Evidence has to be defensible under examination, not just complete. An examining authority can probe how the baseline was derived, how current it is, and why land was excluded. We set out the questions worth rehearsing in five questions the examining authority will ask about your BNG baseline.
For asset owners rather than delivery teams, the same change reads as schedule risk, capital exposure and a thirty-year liability. That version is in a briefing for the board, not the ecology team.
Some teams are considering accelerating to submit before the date and avoid the requirement altogether.
It is worth being honest about the trade-off. An application submitted early but not genuinely examination-ready invites challenge during examination, and time lost there is more expensive than time spent on a baseline. The regime also does not apply to changes to existing DCOs where the original application was not subject to mandatory BNG, so some material change applications will sit outside it regardless.
For most programmes, the more durable answer is to build BNG into the design from concept and pre-application, rather than to race the clock. If you are weighing what can realistically be delivered in the remaining window, what is achievable on an NSIP baseline before November sets out the honest version.
Gentian produces habitat baselines from satellite and aerial imagery, classified to the categories used by the statutory biodiversity metric. On NSIP-scale sites this changes what is possible early in a programme, and our parcel-level habitat accuracy has been independently validated against chartered ecologists.
To be clear about what this is and is not: remote assessment gives you an early, wide, consistent view of habitat across an order limit. It supports route selection, envelope testing, exclusion arguments and the targeting of field effort. It does not replace the ecologist, the field verification, or the statutory submission they sign. Our own work on confidence, which tells you where remote assessment is reliable and where boots are needed, is the part we think matters most.
If you have an NSIP heading for a post-November application and you are not yet sure what your baseline position is, book a scoping call. We will tell you what can be assessed remotely, what cannot, and where the gaps are.