Mandatory biodiversity net gain is about to move into the nationally significant infrastructure project regime. For development consent order applications made on or after 2 November 2026, promoters of NSIPs in England will normally need to demonstrate at least a 10% biodiversity net gain using the statutory framework created by the Environment Act 2021 and the Planning Act 2008.
Defra has now published detailed promoter guidance. The important point for anyone preparing a DCO is that this is not something which can sensibly be left for a requirement to sort out after consent: the boundary, baseline, metric, habitat strategy and securing mechanism all feed back into project design and the application itself.
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NSIP BNG starts with applications made on or after 2 November 2026
The legal machinery arrived earlier than the practical trigger. Section 99 and Schedule 15 of the Environment Act 2021 were brought into force on 7 May 2026 by the Environment Act 2021 (Commencement No. 11) Regulations 2026. Schedule 15 inserted Schedule 2A into the Planning Act 2008 and amended the decision-making provisions in sections 104 and 105.
The practical date for promoters is different. Defra’s biodiversity gain statements and its new NSIP biodiversity net gain guidance apply the mandatory regime to a DCO application made on or after 2 November 2026. It is the date of the application, not the date on which the application is accepted for examination or eventually decided, which matters for this transition.
That distinction is worth getting right. A promoter does not move into the mandatory regime merely because an older application happens to be accepted or examined after 2 November. Equally, an application made on or after that date cannot avoid the regime by pointing to design work or pre-application consultation undertaken beforehand.
What does the 10% objective actually require?
Schedule 2A to the Planning Act 2008 provides for a biodiversity gain objective under which the biodiversity value attributable to the development must exceed the pre-development biodiversity value by at least the specified percentage. The statutory floor is 10%.
For practical purposes, biodiversity value is expressed in biodiversity units and calculated using the statutory biodiversity metric. The calculation does not replace the normal environmental assessment of what habitats are present or what harm a scheme may cause. It sits alongside those duties and policies.
That is why our general guide to biodiversity net gain is still useful background, but the NSIP regime has its own statutory route, gain statements and DCO process.
One metric calculation for the whole DCO project
Defra is explicit that the DCO application should provide a single metric calculation for the development. That remains the position where parts of the NSIP are physically disconnected, fall in different local planning authority areas, or include associated infrastructure and construction compounds away from the main works.
The same approach applies to phased development. In other words, promoters should not assume that a collection of separate works packages can each be treated as a self-contained 10% exercise and then stitched together later.
The BNG boundary can also be different from the DCO order limits. It needs to capture the habitats affected by the development and the habitats being used to deliver the statutory gain. Unimpacted habitat can be excluded where the project ecologist can support that conclusion, but the evidence needs to stand up to scrutiny.
Temporary compounds and separate works areas still count
Temporary does not mean invisible to the metric. The baseline must account for permanent and temporary habitat loss or deterioration arising from the development, enabling and site-preparation works, construction activity, temporary compounds, storage areas, access routes, associated development and expected operational or maintenance impacts.
There is some flexibility where habitat is genuinely temporary. Defra says an impacted habitat may be treated as retained if it is reinstated to its original habitat type and condition within the relevant period: up to five years for low or very low distinctiveness habitat, and up to two years for medium distinctiveness habitat. Even then, the impacted habitat stays in the calculation; it is simply not recorded as a permanent loss if the reinstatement rules are met.
For linear infrastructure in particular, this makes construction logistics a biodiversity issue rather than just a construction-management issue. A haul route, laydown area or cable compound can change the metric outcome and should be tested while the working-width strategy is still capable of changing.
England, the mean low-water mark and the marine boundary
The geographical line needs careful handling. Mandatory NSIP BNG applies to NSIPs, or components of NSIPs, as far as the mean low-water mark. That expressly includes the intertidal zone. It does not extend into the marine environment beyond that point.
So it would be wrong to say that coastal habitat is automatically outside the regime. Intertidal habitat remains within the statutory calculation up to mean low water. Beyond that boundary, the mandatory NSIP BNG calculation does not apply, although marine ecology, compensation and other consenting requirements obviously continue.
Cross-border projects are treated in the same disciplined way. The baseline, BNG boundary plan and statutory metric calculation include only habitat in England, and any habitat creation or enhancement counted towards the mandatory objective must be delivered in England. Voluntary biodiversity enhancement outside England can still be provided, but Defra says it should be calculated separately so that the statutory English position remains clear.
For projects affecting internationally protected sites, BNG does not replace the separate Habitats Regulations Assessment process. Likewise, impacts on Sites of Special Scientific Interest and other protected sites remain subject to their own legal and policy controls.
Follow the mitigation hierarchy before reaching for units
The biodiversity gain statements require the mitigation hierarchy to be addressed. In plain English, the starting point is to avoid significant harm where possible, then mitigate unavoidable harm, with compensation further down the sequence.
This matters because BNG is not a licence to design avoidable ecological harm into a project and simply buy enough units afterwards. The outline biodiversity gain plan needs to explain how the hierarchy has shaped the scheme.
That also creates a direct link with environmental impact assessment and the underlying ecological work. Habitat surveys, EIA mitigation, landscape proposals and BNG delivery need to tell the same story rather than sit in separate consultant silos.
On-site gains, off-site gains and statutory credits
Defra’s delivery hierarchy has three broad routes:
- On-site gains through habitat creation or enhancement within the NSIP BNG boundary
- Off-site gains on other land, secured and registered so the biodiversity units can be allocated to the development
- Statutory biodiversity credits as a last resort after on-site and off-site opportunities have been exhausted
For NSIPs, all on-site habitat creation or enhancement is treated as significant and needs to be secured and maintained. Off-site habitat used for the statutory calculation must be legally secured, registered on the biodiversity gain sites register and allocated to the project.
Statutory credits are deliberately the expensive backstop. The promoter must explain why the objective cannot be met through on-site and off-site provision. A multiplier also applies to the credit system: Defra states that two statutory credits must be bought for every one biodiversity unit required.
The spatial risk multiplier can make remote off-site land expensive
Off-site units do not all carry the same value to a project. The statutory metric applies a spatial risk multiplier where habitat is delivered away from the development.
For area habitat and hedgerow units, the relevant geography uses local planning authority and National Character Area boundaries. Intertidal units use Marine Plan Areas. Watercourse units follow the relevant waterbody and operational catchment geography.
An NSIP boundary may span several LPAs, National Character Areas or Marine Plan Areas. Defra’s guidance says that off-site gains within any of those areas spanned by the project boundary can avoid the spatial penalty for the relevant unit type. Move into neighbouring or more distant areas and the penalty increases the amount of habitat needed for the same effective unit value.
That has an obvious land strategy consequence: a cheap parcel of habitat land a long way from the project may not be cheap once the multiplier is applied.
How must the habitat be secured?
Significant on-site gains can be secured through DCO requirements, a section 106 planning obligation with a local planning authority, or a conservation covenant with a responsible body. The habitat itself should be described in a habitat management and monitoring plan.
Where a section 106 agreement is being considered, promoters will need to think early about which authority is the appropriate counterparty and how that obligation sits alongside the DCO requirements. Large linear projects spanning several authorities make that coordination especially important.
Off-site gains need their own 30-year legal security and registration arrangements. The legal structure is therefore not just a drafting exercise at the end of examination; it can affect land rights, responsible bodies, delivery partners, funding and the project programme.
Thirty years is the minimum, not an afterthought
Significant on-site and off-site habitat creation or enhancement must normally be maintained for at least 30 years. The management period runs from the completion of the relevant habitat enhancement works as defined in the legal arrangement.
The habitat management and monitoring plan needs to set out the management actions, monitoring surveys and reporting. Defra also says that where an NSIP will operate for longer than 30 years, the promoter should continue maintaining the habitat for at least the whole operational period.
That is a substantial asset-management commitment. Promoters need to identify who will own, fund and manage the habitat when the original project team has long since moved on.
BNG cannot sensibly be left as a late DCO requirement
The DCO application itself needs to show how the objective can be met. Defra expects an outline biodiversity gain plan and suitable draft DCO requirements, supported by the project metric and boundary information.
That pulls BNG forward into:
- site selection and route optioneering
- definition of the DCO order limits and the separate BNG boundary
- ecological survey timing and condition assessment
- EIA design and mitigation
- land acquisition and access strategy
- identification of off-site habitat land
- compulsory acquisition strategy where habitat delivery relies on land rights
- DCO drafting, requirements and any planning obligations or conservation covenants
- long-term habitat management, monitoring and funding
If the metric produces an awkward result when the DCO is already frozen for submission, the available solutions may be much more expensive than they would have been six or twelve months earlier.
What should NSIP promoters be doing before 2 November 2026?
For projects heading towards the transition date, I would put the following on the live programme now:
- confirm whether the intended DCO application will be made before or on/after 2 November 2026
- identify the relevant biodiversity gain statement and build it into the application document list
- freeze a defensible survey and baseline strategy with the project ecologist
- run the statutory metric against the emerging project, including temporary works and associated development
- test whether the order limits and BNG boundary give enough room for deliverable on-site habitat
- identify off-site land early and test its spatial-risk position before commercial terms are agreed
- align the BNG work with EIA mitigation, protected-site work and landscape design
- decide how significant gains will be secured and who will discharge the relevant DCO requirements
- prepare the outline gain plan and draft requirements while there is still time to change the project
- budget for 30 years of management, monitoring and reporting rather than only the initial habitat works
The biggest commercial mistake would be to treat the 10% figure as the entire job. The percentage is the headline; the difficult work is making the habitat strategy legally secure, geographically sensible and deliverable throughout the life of a major infrastructure project.
Special cases and exemptions
Irreplaceable habitat is subject to special rules and should not be treated as though ordinary metric units can simply offset its loss. The statutory framework also allows classes of excluded development to be prescribed, so promoters should check the current regulations and the relevant gain statement at the point of submission rather than assuming every special case follows the standard route.
Defra also confirms that the mandatory NSIP BNG regime does not apply to infrastructure authorised through other routes such as Hybrid Bills. For later material or non-material changes to a DCO, the mandatory BNG objective does not automatically operate as though a fresh DCO application had been made, although biodiversity considerations may still be relevant to the change.
Official sources
Created: 28th August 2026 — NSIP biodiversity net gain
