Biodiversity Net Gain (BNG) will become mandatory for Nationally Significant Infrastructure Projects (NSIPs) from 2 November 2026.
The regime will not simply replicate the Town and Country Planning Act (TCPA) approach. Instead, DEFRA has introduced a slightly more flexible and streamlined framework, intended to reflect the unique nature of NSIPs.
The mandatory regime will also not apply retrospectively to an existing Development Consent Order (DCO) (or where changes are made to an existing DCO), where the original application pre-dated the commencement of mandatory NSIP BNG.
The Government’s response to the consultation and the updated BNG statement (see Annex 1 of the response) give a much clearer indication of how BNG for NSIPs is intended to operate in practice.
10% Requirement
Despite some consultation responses calling for a higher percentage requirement for infrastructure projects, the Government has retained the mandatory 10% net gain requirement for consistency across the various types of development.
Streamlined baseline calculations
Only habitats actually affected by the authorised development will need to be included in the baseline calculation (rather than all habitats within the Order Limits).
- This is a significant shift and directly responds to industry concerns that a “whole Order Limits” approach would have a disproportionate impact on larger schemes, particularly where substantial areas of land would remain unaffected by the development.
- ‘Unaffected areas’ can be excluded from the baseline by default, although applicants may still choose to include them voluntarily.
- Further guidance is expected to clarify the requirements for BNG boundary plans and how affected land should be identified in practice.
- This is likely to become a key area of discussion during examination particularly for projects involving cable corridors, highways, pipelines and other extensive linear infrastructure, where the extent of the Order Limits crosses multiple parcels of land.
- The Guidance will be essential for managing the risks of (1) being found to have under-assessed the extent to which there will *any* impact on a given parcel VS (2) applying resources to proving the negative (no effect of any kind) in a way that is not required for any other regime.
Flexibility through outline and phased BNG plans
Applicants will be able to submit outline BNG plans at the pre-application stage, with updated or phased BNG plans submitted later, before commencement of development (or a particular phase). This pragmatic approach reflects the reality that NSIPs may evolve during examination and post-consent, particularly where detailed design, construction methodologies and temporary land requirements continue to develop.
Importantly, any shortfall in biodiversity gains can be secured later in the process once the final impacts on habitats are known. This flexibility is likely to be welcomed by promoters, particularly on complex phased schemes where final habitat impacts cannot realistically be confirmed at the application stage.
Temporary habitat impacts
The NSIP BNG regime also introduces a more nuanced approach to temporary habitat impacts. Offset for temporary impacts will generally not need to be secured for 30 years where habitats are reinstated following construction. This is particularly relevant for projects involving temporary possession, compounds, haul roads and working areas which are later restored and returned to landowners.
In addition, DEFRA has extended the reinstatement period for habitats of low and very low distinctiveness from two years to five years, allowing these habitats to continue to be treated as retained habitats for BNG purposes where they are removed but the reinstated within the period. This is another example of DEFRA adapting the regime to reflect the practical realities of delivering infrastructure.
Off-site v On-site
The revised approach allows promoters to rely on off-site gains alongside on-site delivery. Whilst the mitigation hierarchy remains, promoters will have greater flexibility to rely on off-site biodiversity gains earlier in the process, rather than being expected to exhaust all onsite opportunities first.
This reflects the concerns raised during the consultation, that many NSIPs, particularly linear projects, have limited opportunities to deliver meaningful onsite gains within constrained operational corridors.
The revised approach is also intended to support the off-site BNG market by giving promoters greater confidence that off-site delivery can form a legitimate part of the overall BNG strategy from the outset.
Approval of post-consent BNG Plans
Any of the following are now proposed as downstream approvers:
- the host local planning authority;
- a lead local planning authority; or
- the Secretary of State in consultation with relevant LPAs.
The Government has also acknowledged concerns around local authority resourcing and ecological expertise, particularly given the scale and complexity of NSIP schemes. Whether LPAs will have sufficient resources to discharge these obligations efficiently in practice will remain to be seen and is likely to vary significantly between authorities.
Wider BNG reforms also on the horizon
Alongside the NSIP reforms, the Government has also announced a wider package of changes to the BNG regime, which is expected to be rolled out by end of July 2026, subject to parliamentary scheduling.
These include:
- a new 0.2 hectare exemption;
- removal of the self-build/custom-build exemption;
- exemptions for temporary permissions of up to five years;
- greater flexibility for minor developments to rely on off-site gains;
- reforms relating to Open Mosaic Habitat;
- changes to the biodiversity metric and spatial risk multipliers; and
- a move away from Excel-based tools towards a more integrated digital system.
There is also a live consultation running until June 2026 in relation to a proposed exemption for residential brownfield development.
These changes are aimed at simplifying the regime, reducing administrative burdens and addressing many of the practical issues raised by developers, consultants and local authorities since mandatory BNG was introduced under the TCPA regime.
Final thoughts
Overall, whilst the Government has retained alignment between the TCPA and NSIP regimes in terms of the 10% BNG requirement, the proposed NSIP framework represents a clear move towards a more flexible and infrastructure-focused approach to delivery.
Whilst some practical questions remain, particularly around guidance, baseline assessments and post-consent approvals, the revised framework is likely to be welcomed by promoters as a more pragmatic approach to balance biodiversity enhancement with the Government’s wider infrastructure and growth agenda.
