Last updated: September 18, 2026
Quick Answer
Biodiversity Net Gain becomes mandatory for Nationally Significant Infrastructure Projects (NSIPs) in England from 2 November 2026, delayed from the original May 2026 date [1][2]. NSIP developers submitting a Development Consent Order (DCO) application from that date must demonstrate at least 10% biodiversity gain against pre-development habitat value, following the relevant sectoral biodiversity gain statement [6][10]. Separately, changes effective 6 August 2026 introduced a 0.2-hectare small-site exemption, removed the self/custom-build exemption, and disapplied the biodiversity gain hierarchy for minor development.
Key Takeaways
- NSIP BNG becomes mandatory on 2 November 2026, six months later than the May 2026 date originally proposed [1][2][9].
- NSIPs must achieve a minimum 10% biodiversity gain, calculated only against habitats actually impacted by the development, not the full site boundary [3][6].
- A new "BNG boundary" concept captures both permanent and temporary habitat impacts for NSIP baselines [9].
- From 6 August 2026, sites under 0.2 hectares are exempt from BNG if no priority habitat is affected.
- The self-build and custom-build exemption has been removed, bringing individual house-builders into scope.
- For minor development, the biodiversity gain hierarchy no longer applies, so offsite gains carry equal weight to onsite gains.
- NSIP BNG is far more front-loaded than town-and-country planning BNG, requiring biodiversity assessment work during pre-application.
- CIEEM and CLA both stress early ecological input to avoid delay at the DCO examination stage [9].
What Is Biodiversity Net Gain and Why Does It Matter Now
Biodiversity Net Gain (BNG) is a legal requirement that development leave biodiversity in a measurably better state than before construction started, calculated using a standardised metric. It matters now because, from 2 November 2026, the requirement extends beyond conventional planning permissions to cover Nationally Significant Infrastructure Projects, closing a gap that had exempted major energy, transport, and water schemes [1][4].
BNG works by comparing pre-development habitat value against post-development value, expressed in biodiversity units. Developers must show a net increase, usually a minimum of 10%, through some combination of:
- Retaining and enhancing existing onsite habitat
- Creating new habitat onsite
- Buying registered offsite biodiversity units
- Purchasing statutory biodiversity credits as a last resort
For ecological consultants, September 2026 is a pivotal month: guidance updated through the summer is now settling into practice, and firms working across both town-and-country and NSIP projects need to run two parallel compliance frameworks side by side.
How Will the November 2026 NSIP Changes Affect Your Development Project
If your project is an NSIP requiring a DCO application submitted on or after 2 November 2026, you must meet the biodiversity gain objective set out in the gain statement relevant to your sector, or consent cannot be granted [1][6]. This is a hard legal gateway, not a planning condition to be tidied up later.
The legal basis sits in section 99 and Schedule 15 of the Environment Act 2021, which inserted Schedule 2A and revised sections 103 to 105 of the Planning Act 2008 [6]. Practically, this changes the sequence of work compared with standard planning BNG:
- Biodiversity baseline surveys must happen during pre-application, not after consent
- Gain statements linked to the relevant National Policy Statement (NPS) set sector-specific expectations, with a cross-cutting statement covering NSIPs without an NPS [2]
- The Secretary of State must be satisfied the gain objective is met before granting the DCO [6]
- Scope only applies to England, out to the mean low-water mark including the intertidal zone; marine elements beyond that are excluded [6]
Decision rule: if your DCO application is submitted before 2 November 2026, current rules apply; if submitted on or after that date, the NSIP BNG regime is mandatory regardless of when pre-application work began [1][2].
What Are the New Biodiversity Net Gain Requirements for UK Developers After 6 August 2026
Changes taking effect on 6 August 2026 reshaped BNG for smaller and conventional developments ahead of the NSIP rollout, and developers need to track both sets of changes together. Three shifts stand out for anyone running sites under Town and Country Planning rules.
| Change (from 6 August 2026) | What it means in practice |
|---|---|
| 0.2-hectare small-site exemption | Sites under 0.2 hectares are exempt from BNG if no priority habitat is affected; larger or priority-habitat sites still need full assessment |
| Gain hierarchy disapplied for minor development | Offsite gains no longer rank below onsite gains for minor schemes; developers can choose offsite units without justifying why onsite delivery was unfeasible |
| Self/custom-build exemption removed | Individual and custom-build house plots now require a BNG assessment, closing a route many small builders previously relied on |
For planners assessing applications, this means checking site area and priority habitat status early, since a wrongly assumed exemption can stall validation. See our related guidance on what you need for a biodiversity net gain report for the documentation planners should expect.
How Do You Calculate Biodiversity Net Gain for Your Site
BNG is calculated using the statutory biodiversity metric, which scores habitat parcels for distinctiveness, condition, and area (or length, for linear features), then compares baseline and post-development totals. The output is a percentage change in biodiversity units, and NSIPs need at least +10% [6].
The calculation steps are:
- Survey and classify all habitats within the BNG boundary, including temporarily affected land [9]
- Score each habitat parcel using the metric's condition and distinctiveness criteria
- Model the post-development scenario, including retained, enhanced, and newly created habitat
- Add any offsite units or statutory credits needed to close the gap
- Confirm the net change meets or exceeds the required percentage
A common edge case: linear NSIP schemes such as pipelines or transmission lines often disturb land temporarily during construction. The BNG boundary concept specifically captures these temporary impacts, so they must be included in the baseline even where the land is restored afterward [9]. For a fuller walk-through, see what is in a biodiversity net gain assessment.
BNG vs Environmental Impact Assessment: What's the Difference
BNG and Environmental Impact Assessment (EIA) are separate legal processes that overlap in evidence but differ in purpose: EIA assesses the wider environmental effects of a project, while BNG specifically measures and mandates a quantified biodiversity outcome. A project can pass EIA scrutiny and still fail to meet its BNG gain objective.
Key distinctions:
- EIA covers air, noise, water, landscape, and ecology broadly; BNG is narrowly focused on habitat units
- EIA is a process of disclosure and mitigation; BNG sets a binding numerical target
- For NSIPs, Defra guidance confirms BNG should be integrated with EIA and design work rather than run as an afterthought [8]
Ecological consultants should treat baseline ecology surveys as shared evidence feeding both processes, cutting duplicate site visits.
Which Projects Are Exempt From Biodiversity Net Gain Requirements
Certain developments remain outside BNG scope, though the list has narrowed considerably since August 2026. Current exemptions include sites under 0.2 hectares with no priority habitat, householder applications that don't involve new build on greenfield land, and de minimis development types set out in the general BNG guidance [4][10].
Notably no longer exempt:
- Self-build and custom-build homes, following the August 2026 change
- NSIPs, once the November 2026 mandate takes effect
Common mistake: assuming an NSIP component located offshore is automatically exempt. Only the marine elements beyond the mean low-water mark and intertidal zone fall outside scope; intertidal habitat is still counted [6].
What Does BNG Compliance Cost, and What Happens If You Don't Meet Targets
BNG compliance costs vary widely by site type, habitat baseline, and whether gains are delivered onsite or bought as offsite units or statutory credits; there is no fixed national fee, but statutory biodiversity credits are deliberately priced as a costly last resort to discourage overreliance on them. Defra's impact assessment for NSIP BNG sets out the expected cost and benefit balance behind the 10% threshold, reflecting feasibility for large infrastructure promoters [12].
If targets aren't met:
- For standard planning permissions, the local planning authority can refuse or condition consent until the metric shows compliance
- For NSIPs, the Secretary of State cannot grant a DCO unless satisfied the gain objective in the relevant gain statement is met [6]
This makes NSIP non-compliance a consent-blocking issue rather than a post-approval enforcement matter. See our cost of biodiversity units guide for indicative unit pricing.
Can You Pay Into a BNG Habitat Bank Instead of Creating Habitat On Site
Yes, developers can purchase registered offsite biodiversity units from a habitat bank instead of, or alongside, creating habitat onsite, and for minor development this route no longer needs to be justified against the gain hierarchy [3][8]. For NSIPs, offsite units and statutory biodiversity credits are explicitly part of the toolkit once BNG becomes mandatory in November 2026 [3].
Practical notes:
- Offsite units must come from a registered biodiversity gain site
- Water-related NSIP impacts must generally be addressed within the relevant catchment, even when aggregating offsite gains across local planning authority areas [9]
- Habitat banks suit developers without spare onsite land, or projects where onsite habitat creation risks fragmenting a functioning site layout
Explore buying biodiversity units or selling biodiversity units if you're weighing this route as a buyer or a landowner supplier.
Common Mistakes, Timelines, and Who Needs to Be Involved
The most common BNG mistake is treating it as a late-stage planning condition rather than a design input, which is precisely what the front-loaded NSIP regime now punishes. Ecological baseline surveys are seasonally constrained, so leaving them until after consent is granted risks a 12-month delay for the next survey window.
Realistic timelines:
- Baseline ecological surveys: typically span one full survey season, sometimes longer for protected species
- Metric calculation and design iteration: several weeks to a few months, depending on habitat complexity
- NSIP pre-application biodiversity assessment: should begin alongside scoping, well before DCO submission
Who should be at the table early: ecological consultants, planning consultants, landscape architects, and the local planning authority (for offsite unit registration). CIEEM guidance for practitioners stresses that ecologists need visibility of the whole BNG boundary, including temporary works areas, from the earliest design stage. For architects specifically, see how architects can solve biodiversity net gain.
What Habitats Count Most Toward Biodiversity Net Gain
Habitats scoring highest under the statutory metric are those with high distinctiveness and good condition, such as ancient woodland, species-rich grassland, and wetland, because these contribute more biodiversity units per hectare than low-distinctiveness habitat like amenity grassland. For NSIPs, only habitats actually impacted by the development count toward the calculation, not the entire red-line boundary [3][9].
Practical implications:
- Retaining high-distinctiveness habitat onsite is usually cheaper than replacing it through offsite units
- Priority habitat presence is the trigger that removes the 0.2-hectare small-site exemption
- Temporarily disturbed high-distinctiveness habitat must still be counted in the baseline for NSIP BNG boundaries [9]
For a broader primer, see biodiversity net gain explained and how to achieve 10% biodiversity net gain.
Frequently Asked Questions
When exactly does BNG become mandatory for NSIPs?
From 2 November 2026, for any DCO application submitted on or after that date, following the sectoral biodiversity gain statement relevant to the project [1][2].
Why was the NSIP BNG start date delayed from May 2026?
Defra laid sectoral gain statements and statutory instruments through May and June 2026, and a 4 June 2026 update confirmed the later 2 November 2026 date to give NSIP promoters more lead-in time [2][6].
Does the 0.2-hectare exemption apply to NSIPs?
No. The 0.2-hectare small-site exemption, effective from 6 August 2026, applies to conventional town-and-country planning applications, not NSIPs, which follow their own sectoral gain statements [3][6].
Can self-build homes still avoid a BNG assessment?
No. The self/custom-build exemption was removed as part of the August 2026 changes, so individual house plots now require a BNG assessment unless another exemption applies.
Is the biodiversity gain hierarchy still relevant for major schemes?
Yes. The disapplication of the hierarchy for minor development, from August 2026, does not extend to major development or NSIPs, where onsite delivery is still generally preferred where feasible [3][9].
What happens if temporary construction impacts aren't included in an NSIP baseline?
The application risks failing the gain objective assessment, since the BNG boundary concept requires both permanent and temporary habitat impacts to be captured in the baseline [9].
Conclusion
BNG for NSIPs moves from proposal to legal requirement on 2 November 2026, and the accompanying August 2026 changes to small-site exemptions, the gain hierarchy, and self-build rules mean almost no development scale escapes some form of BNG obligation now. Developers running NSIP projects should start biodiversity baseline work at scoping stage, not after DCO submission, since the Secretary of State cannot grant consent without a satisfied gain objective [6]. Ecological consultants should map the full BNG boundary, including temporary works areas, and planning teams should double-check exemption eligibility rather than assume it. For practical next steps, review 8 things planners need to know about BNG and speak to an ecological consultant before your next scoping report is finalised.
References
[1] Biodiversity Net Gain Nationally Significant Infrastructure Projects – gov.uk
[2] Biodiversity Net Gain For Nsips Gain Statements Laid And Guidance Published – defraenvironment.blog.gov.uk
[3] Biodiversity Net Gain For Major Infrastructure Projects New Guidance – defraenvironment.blog.gov.uk
[4] Biodiversity Net Gain Guidance For Developers Land Managers And Authorities – gov.uk
[6] Nationally Significant Infrastructure Projects Biodiversity Gain Statement For Water Resources Accessible Version – gov.uk
[8] Biodiversity Net Gain Whats Changing And What It Means For You – defraenvironment.blog.gov.uk
[9] Key Changes Confirmed To Biodiversity Net Gain – cla.org.uk
[10] What You Can Count Towards A Developments Biodiversity Net Gain – gov.uk
[12] Impact Assessment for BNG in NSIPs, 2026 – gov.uk