Government confirms mandatory biodiversity net gain for NSIPs from May 2026 – consultation now open

The Government has announced its intention to introduce mandatory biodiversity net gain (“BNG”) for nationally significant infrastructure projects (“NSIPs”) from May 2026 – six months later than the originally anticipated implementation date of November 2025. The Government consultation is now open for responses until 24 July 2025.

This development forms part of a broader suite of reforms aimed at improving the efficiency and effectiveness of the planning system, including the measures proposed in the Planning and Infrastructure Bill (as summarised in our article here) and updates to the relevant National Policy Statements. The Government recognises the positive steps already taken by many NSIP promoters to deliver biodiversity gains through their schemes and seeks to build on this momentum by introducing a consistent, mandatory framework.

The Government is proposing a ‘core’ approach to BNG for all NSIP types to maintain consistency across sectors and reduce complexity for developers and decision-makers. Central to this is a draft ‘model text’ for a core biodiversity gain statement, which, once finalised, is intended to be replicated and applied to each NSIP sector. This biodiversity gain statement is intended to have the same effect as if included in the relevant National Policy Statement, and will be incorporated into the relevant National Policy Statements at their next review.

Whilst the BNG regime for NSIPs is intended to broadly replicate the existing regime for Town and Country Planning Act 1990 (“TCPA”) developments, there are a few key differences proposed in the consultation, recognising the unique challenges posed by NSIPs such as the scale of development boundaries, post-consent design changes and the use of land temporarily during construction. 

Key Proposals

Scope

• Mandatory BNG will apply to all DCO applications submitted under section 37 and determined under sections 104 or 105 of the Planning Act 2008, including those made following a section 35 Planning Act 2008 direction that the development is to be treated as an NSIP.
   
• BNG will apply to NSIPs, or components of NSIPs, onshore in England up to the mean low-water mark, including all temporary, permanent, and associated development within the DCO site boundary (‘order limits’).

Calculating BNG

• The statutory biodiversity metric used for TCPA developments will also apply to NSIPs, ensuring consistency across the planning regimes and enabling NSIPs to purchase biodiversity units from the existing off-site market.
   
• As with TCPA developments, the core objective is that the biodiversity value attributable to a development must exceed the pre-development biodiversity value of the on-site habitat by at least 10%, evidenced in a biodiversity gain plan.
   
• All habitats within the entire development site boundary (i.e. the ‘order limits’) are proposed to be included in the pre-development biodiversity value calculation.
   
• The Government recognises that NSIP boundaries may be significantly larger than the actual construction area and is therefore seeking evidence on alternative options from developers.

Exclusions

• Projects in the marine environment beyond the intertidal zone are excluded. Whether the Government will develop Marine Net Gain will be decided in due course.
   
• The BNG requirement will not apply retrospectively to applications for changes to DCOs where the original application was submitted or granted before May 2026 (mirroring the approach for TCPA developments).
   
• The BNG objective does not apply to irreplaceable habitats, although existing protections and compensation requirements remain. Where loss or deterioration is unavoidable, bespoke compensation must be agreed, and statutory biodiversity credits cannot be used.

Delivering BNG

• As with the TCPA regime, BNG for NSIPs can be delivered through: (1) on-site gains, (2) registered off-site gains allocated to the development, and/or (3) statutory biodiversity credits.
   
• However, it is proposed that NSIP applicants can deliver BNG on-site or off-site in the first instance, without being required to prioritise on-site delivery. This is to avoid incentivising compulsory acquisition of additional land solely for BNG purposes.
   
• The existing biodiversity gain site register will be used for NSIPs to maintain consistency, and as with the TCPA regime any significant on-site enhancements and all off-site gains must be legally secured for at least 30 years.

Temporary use of land

• The Government recognises that there may need to be a bespoke policy for land used temporarily during construction (i.e. land that is not required for the permanent operation of the development). Without a bespoke policy, such land would be included in the pre-development biodiversity value and would be subject to the BNG requirement – which may be difficult to agree with landowners who may be unwilling to restrict the use of their land for 30 years. The consultation therefore seeks views on whether such a bespoke policy for temporary construction land is required.

Evidence for submission and decision-making

• Applicants will be required to submit a biodiversity gain plan and a completed biodiversity metric calculation as part of their DCO application, demonstrating how the biodiversity gain objective will be met. The biodiversity gain plan must include the information set out in the draft ‘model text’. The proposed ‘model text’ can be found at Annex 1 to the consultation document.
   
• To accommodate post-consent design changes that may impact BNG calculations, it is proposed that an updated biodiversity gain plan and calculations are submitted to the relevant local planning authority for approval post-consent. Where NSIPs are delivered in phases, this process may also be phased accordingly.

Next Steps

• The consultation closes on 24 July 2025.
   
• A final stage impact assessment will be produced before BNG is brought into force for NSIPs. The consultation welcomes suggestions for any additional evidence to inform future analysis, such as estimated cost to NSIP developers, the expected proportion of BNG that will be delivered on-site, and the impact of mandatory BNG on NSIP development practices.
   
• The Government also intends to publish further guidance on a range of topics relevant to the NSIP process, including schemes crossing multiple boundaries, securing gains, and phased delivery.

Conclusion

The introduction of mandatory BNG for NSIPs marks a significant shift for the planning and delivery of major infrastructure in England. The proposals aim to provide clarity and consistency with the existing BNG regime for TCPA developments, while recognising the unique challenges of NSIPs. The proposed flexibility to deliver BNG either on-site or off-site from the outset, alongside the proposed alignment with the existing statutory metric and gain site register, will help streamline compliance and reduce the risk of unintended consequences, such as unnecessary land acquisition.

For developers, promoters, and landowners involved in NSIPs, this consultation presents a crucial opportunity to shape the final policy, particularly on issues such as the treatment of temporary land, the calculation of pre-development value, and the practicalities of securing gains for 30 years. The requirement to submit and update biodiversity gain plans, and the potential for phased approval, will also have significant implications for project programming and risk management.

The Government is also consulting on improving the implementation of BNG for minor, medium and brownfield developments, which we will be commenting on separately.

This article was co-authored by Abi Hill, Trainee Solicitor, in the Planning team at CMS.