BNG for NSIPs – Impact of Biodiversity Gain Statements and Guidance

The Government has laid before Parliament the long-awaited biodiversity gain statements which provide key details on how the biodiversity net gain (BNG) regime will apply to nationally significant infrastructure projects (NSIPs).

BNG, introduced under the Environment Act 2021, requires projects to achieve at least a 10% uplift in biodiversity value against pre-development habitat. It already applies to most Town and Country Planning Act 1990 (TCPA) developments.

For NSIPs, BNG will (by virtue of the coming into force of the relevant parts of the Planning and Infrastructure Act 2025) become mandatory for applications made on or after 2 November 2026, save for excluded developments. The Secretary of State will not grant development consent unless satisfied that the biodiversity gain objective is met, though Development Consent Order (DCO) requirements securing delivery may suffice.

Applicants should embed BNG into project planning from the outset, including through an outline biodiversity gain plan, the statutory biodiversity metric, and mechanisms to secure delivery through the DCO.

The statements (available here) detail how to calculate, deliver, and report on BNG across each relevant NPS. While sector-specific, their content is broadly identical. This article addresses the consistent points within those statements that are applicable across all NSIP types.

Alongside the statements, the Government has also published guidance relating to pre-application steps for NSIPs and the content of a DCO, both of which address BNG-related matters that applicants must consider when preparing their applications.

Scope of BNG for NSIPSs

The BNG regime applies to NSIPs in England requiring development consent under the Planning Act 2008, including projects brought into that regime by direction of the Secretary of State. Where boundaries extend beyond England, only English components are subject to the requirement. The requirement applies to components as far as the mean low-water mark, including the intertidal zone, but excludes marine elements beyond that point.

It is of note that the legislation introducing BNG into the NSIP regime provides for “excluded development” which will not be subject to the biodiversity gain objective. Schedule 2A, paragraph 1(2) of the Planning Act 2008 includes provisions for development to be excluded from the biodiversity gain objective through regulations made by the relevant Secretary of State. However, no regulations have yet been made at the time of writing.

Pre-Application Steps, evidence submission and DCO Content

While there is no statutory requirement for applicants to engage or consult during the pre-application stage under the new regime, applicants may choose to do so in order to support the evolution of their proposals. Applicants are also encouraged to share their indicative BNG requirement (calculated using the statutory biodiversity metric) and proposed delivery approach with the Planning Inspectorate and relevant stakeholders, to front-load key issues ahead of examination.

As part of the DCO application, applicants must submit an outline biodiversity gain plan setting out the strategy for delivering the statutory biodiversity gain objective of at least 10%. The plan must include ecological input, baseline position, BNG boundary plan, completed statutory metric calculation, arrangements for maintaining significant on-site gains, details addressing irreplaceable habitat, the mitigation hierarchy, the proposed mix of delivery mechanisms, and all other matters set out in the relevant biodiversity gain statement. The draft DCO must also include requirements to secure the biodiversity net gain objective, covering monitoring, reporting and adaptive management. The body responsible for discharging each requirement must be named, and requirements must secure approval of updated biodiversity gain plans and evidence of secured units before operation.

Mitigation hierarchy and calculating BNG

BNG must be applied according to the mitigation hierarchy: developers should first avoid significant harm, then mitigate impacts where harm cannot be avoided, with compensation used only as a last resort. This approach mirrors that of the existing TCPA regime. Applicants must explain in their outline biodiversity gain plan how their proposals follow this hierarchy.

As is currently required under the TCPA, applicants must use the statutory biodiversity metric to assess biodiversity value. The metric should not be applied in purely mechanical terms: it must be applied alongside wider ecological consideration and professional judgement. The statutory biodiversity metric calculation tool must be used to demonstrate proper application.

Pre-development biodiversity value 

A baseline assessment determines the scale of BNG required. The assessment must capture pre-development biodiversity value of habitats within order limits that will be negatively affected (temporary or permanent loss/deterioration), plus habitats that will be enhanced or created on-site. Unaffected habitats need not be included, though applicants may choose to include them.

Applicants must prepare a BNG boundary plan showing the full order limits and distinguishing impacted areas, areas contributing to BNG, retained habitats included in the baseline and unaffected habitats. Where design uncertainty exists, the baseline must reflect a realistic worst-case assessment of habitat loss or deterioration, including construction, enabling works, access routes and associated development.  

Delivering BNG

NSIPs can deliver BNG using on-site gains, off-site gains, or a combination of both. Unlike the regime under the Town and Country Planning Act, there is no requirement to prioritise on-site options before turning to off-site gains; both are equally available.

On-site gains are measured by calculating the projected post-development biodiversity value using the statutory biodiversity metric. This covers habitats that are kept, restored, improved or newly created on-site, provided they are properly maintained and secured (see below).

Statutory biodiversity credits are a last resort. An applicant wishing to use credits must demonstrate in its biodiversity gain plan that on-site and off-site options were insufficient to meet the biodiversity gain objective.

Securing On-Site Gains

Where on-site habitat is created or enhanced (rather than simply reinstated), this counts as a significant on-site gain. These must be:

• maintained for at least 30 years from when the habitat works are completed;
• supported by a habitat management and monitoring plan covering the full 30-year period; and
• legally secured for the 30 years by one of the following:
  • a requirement in the DCO;
  • a planning obligation in a section 106 agreement; or
  • a conservation covenant.

Habitats that are simply retained, or temporarily disturbed and then reinstated, are non-significant gains. They still count towards the metric but do not need to be formally secured.

Securing Off-Site Gains

Off-site gains must be:

• registered on the biodiversity gain site register, with the allocation to the development recorded on that register; and
• legally secured for 30 years by one of the following:
  • a planning obligation in a section 106 agreement; or
  • a conservation covenant.

Unlike on-site gains, off-site gains cannot be secured solely through DCO requirements; a separate legal agreement is always needed.

Irreplaceable Habitats

Irreplaceable habitats are those which would be technically “very difficult, or would take a very significant time, to restore, recreate or replace once destroyed”.  Such habitat must be recorded but its value is excluded from the baseline and BNG calculation unless enhancement is proposed. 

Loss or deterioration of such habitat therefore requires bespoke compensation linked to the original habitat type, cannot rely on statutory biodiversity credits, and cannot count towards the 10% objective. Where non-irreplaceable habitats are also present, the 10% objective still applies to those areas.

In respect of these habitats, the requirement to provider BNG also does not replace existing protections, such as under habitats legislation.

Conclusion

BNG should be treated as a core consenting risk for NSIPs, not a late-stage workstream. DCO applications made on or after 2 November 2026 must demonstrate the required biodiversity gain and secure its delivery, as well as following the methodologies set out within the biodiversity gain statements and guidance.

The priority is to build robust ecological baseline evidence, BNG boundary planning and mitigation hierarchy decisions into site selection and design from the outset. Early engagement and testing of on-site and off-site delivery options will also help manage examination risk and avoid delivery constraints, as well as allowing BNG considerations to be aligned with site assembly and CPO strategies, environmental assessments and mitigation plans.

Co-authored by Hareni Ayadurai (trainee in the Planning Team)