Building Greener: Biodiversity Net Gain (BNG) comes to Nationally Significant Infrastructure Projects (NSIPs)
Mandatory BNG requirements apply to applications made on or after 2 November 2026 relating to large-scale developments of strategic national importance known as NSIPs. This will be a significant expansion to the scope of the BNG regime as well as the extent of biodiversity requirements which NSIPs must follow. NSIP promoters will need to be sufficiently prepared to incorporate BNG requirements to ensure compliance and to avoid significant practical challenges. This article sets out the legislative framework behind the BNG, NSIPs and the wider development and legal considerations which developers, contractors and consultants alike should be considering.
BNG legislative framework
BNG was made mandatory under Schedule 7A of the Town and Country Planning Act 1990 (TCPA 1990) (as inserted by Schedule 14 of the Environment Act 2021). This means that developers must now deliver a BNG of 10% against the development's benchmark, and any gain above the benchmark can be banked as excess biodiversity units to offset other developments. The key principle being that habitats for wildlife must be "left in a measurably better state than they were before the development."
Developers must submit a biodiversity gain plan (BGP) to demonstrate how they will meet the mandatory 10% target. This is a post-planning permission document, which must be submitted after planning approval to discharge mandatory BNG conditions.
The BNG regime allows some flexibility in how a developer can achieve BNG, including:
1) creating the biodiversity on-site and within the red-line boundary of a development;
2) making off-site biodiversity gains on their own land outside the development site, or buying off-site biodiversity units on the market; or
3) purchasing statutory biodiversity credits from the government, who will use the revenue to invest in habitat creation in England.
While all three options can be combined, a developer must follow the steps in order of the biodiversity gain hierarchy above. Delivering the biodiversity gains on-site is the BNG regime's primary aim.
Some developments are exempt from the mandatory BNG requirements. For example, a development that does not impact a priority habitat is exempt. Additionally, planning applications made by householders (including home extensions or conservatories) are exempt. Other exemptions include: any HS2-related developments, urgent crown developments and those that are granted planning permission by a development order. Developers need to confirm whether or not a development is exempt from BNG when a planning application is submitted. Further information on exemptions can be found in our previous article: Biodiversity Net Gain: February 2023 Update.
The 2025 consultation: BNG meets major infrastructure
The previous consultation Biodiversity net gain for nationally significant infrastructure projects ran from May 2025 to July 2025 and requested views on the implementation of BNG for NSIPs. The outcome was published in April 2026 and this determined that BNG will apply to NSIP applications made on or after 2 November 2026, with the aim of delivering infrastructure alongside protecting and restoring nature at scale.
In the Planning Act 2008, NSIPs are defined as large-scale major development projects in England or Wales falling into five general categories: energy, transport, waste, waste water and water. The projects could range from power generating stations and offshore wind farms to reservoirs and new roads.
However, rather than seeking planning approval from the local planning authority, consent must be obtained from the government directly. If a development meets the threshold described above, it will require a Development Consent Order (DCO). A DCO is similar to planning permission but can also include listed building consent and compulsory acquisition powers. NSIP applications are handled by the Planning Inspectorate on behalf of the Secretary of State.
NSIPs and BNG: How will this all work in practice?
As of 2 November 2026, a DCO will not be granted unless a BGP and the supporting Defra Biodiversity Metric calculations are provided as part of the application. The BGP functions similarly to the document required under the TCPA 1990. This is being introduced by Schedule 15 to the Environment Act 2021 (which inserts Schedule 2A into the Planning Act 2008).
The BNG baseline date, 30 January 2020 (the date the Environment Bill was first introduced into Parliament) prevents a developer or landowner from deliberately clearing, degrading or damaging habitats on their land before applying for a DCO. This would artificially lower the pre-development biodiversity value, making it easier to demonstrate a 10% net gain.
Delivery of the 10% net gain can be on-site, however this will be impractical for most NSIPs given the nature of the works and scope of the project. Therefore, off-site net gains are expected to constitute the majority of BNG provision for most NSIPs. Off-site gains must be legally secured (for example, in a conservation covenant or through planning obligations) and registered on the dedicated NSIP BNG Site Register, which mirrors the standard BNG site register operated by Natural England for TCPA 1990 planning permissions. Registration is a pre-condition to off-site units counting towards a project's BNG requirement. Note that any biodiversity enhancements and creation to count towards the BNG for a development must be delivered in England.
Exemptions for NSIPs are purposefully limited and are expected to include only irreplaceable habitats, small or negligible biodiversity impacts that may fall below the threshold, and previously developed land with no priority habitats. Marine or offshore elements of NSIPs remain a grey area, as the standard Defra metrics do not apply to tidal habitats in the same way.
The mandatory maintenance period for BNG is 30 years, running from the date the habitat creation or enhancement works are completed. This means that active management is required to ensure the habitat achieves and sustains the biodiversity value predicted in the metric. The Habitat Management and Monitoring Plan (HMMP) is the document that governs the 30-year obligation and must be approved before development commences (as part of the BGP approval process). It is important to note that the maintenance period is not retrospective for DCOs submitted prior to May 2026.
Development and legal considerations
The extension of mandatory BNG to NSIPs is a welcome step towards regulatory consistency. By aligning the NSIP regime with the existing framework under the TCPA 1990, developers and their advisors can draw on established principles and processes, including the BGP methodology and the Defra Biodiversity Metric, when preparing DCO applications. This alignment should, in principle, reduce uncertainty and promote a uniform approach to the enhancement of biodiversity across all scales of development.
However, the introduction of mandatory BNG obligations for NSIPs raises significant practical concerns. Major infrastructure projects are already subject to considerable cost pressures arising from supply chain constraints, escalating planning costs and persistent inflationary pressures. The requirement to deliver a minimum 10% net gain in biodiversity adds a further layer of complexity and expense. Given the scale and nature of most NSIPs, on-site delivery of BNG will often be impracticable, meaning that developers will be heavily reliant on securing off-site biodiversity units, a market that remains relatively nascent and may lack sufficient supply to meet demand. In addition, the practicality of managing and enforcing the 30-year maintenance obligations associated with off-site habitat creation will have to be streamlined, particularly where responsibility for long-term stewardship must be allocated across multiple parties and landholdings.
The legal implications for contractors are wide-ranging. Contractors engaged on NSIP projects must recognise that delivering measurable biodiversity outcomes is of increasing importance and, whilst the statutory obligation sits with the NSIP promoter, contractors will have a critical role to play.
Whereas biodiversity implications may previously have received limited attention during the project design stage, the nature of the BNG requirements now means that construction methodologies, temporary works, access routes and site compounds will all need to account for biodiversity implications from the outset. This is essential to avoid harmful impacts arising from unauthorised clearance of vegetation, damage to retained habitats or failure to implement ecological protection measures properly. Main infrastructure contractors may have limited experience in delivering ecological works and consider it appropriate to sub-contract off-site or on-site work instead.
The requirement to provide an outline biodiversity gain plan as part of the DCO application prior to works commencing introduces additional time-related pressures to the construction programme. As most off-site BNG works need to be delivered prior to any habitat loss on the main site, the sequencing of the critical path must account for this and ensure off-site works are not deprioritised. This will also remove a worst-case scenario of the main works removing the existing biological habitat prior to the off-site works being delivered and the contractor going insolvent, leaving a lengthy gap in ecological provision. The contract will need to include suitable drafting to address BNG-related compensation events or extensions of time- contractors will seek to ensure any programme risks sit with the NSIP promoter, particularly where delay arises from a late application by the NSIP applicant or a prolonged response by the relevant deciding authority.
NSIP promoters will need to be cognisant of the speculative nature of delivering off-site ecological works with the prevalent risk of invasive species or unknown soil conditions and should anticipate contractors pricing in the risk quite heavily or by extended use of provisional sums. NSIP promoters may also not own this land at the time of the construction contract tendering and so the opportunity for the contractor to investigate the area fully may not be possible and result in a contract sum which has limited cost certainty.
Given that many infrastructure contractors bear significant design responsibility when delivering NSIP projects, the contractor is likely to be responsible for designing key BNG features such as green corridors, soft and hard landscaping and sustainable drainage systems. As these design solutions will form a core component of the post-development BNG score, a contractor's exposure to professional liability claims will increase substantially if a project fails to achieve the biodiversity outcome aligned with the approved metric calculations. Contractors should therefore maintain comprehensive records of biodiversity-related deliverables in the event of a dispute, including ecological inspection reports, planting records, as-built photographs and baseline monitoring data.
Whilst contractors are unlikely to retain any long-term responsibility for BNG maintenance, monitoring and reporting arrangements, they will have an important role to play during the defects liability period. The contract drafting will need to delineate clearly which aspects of the BNG deliverables fall within the contractor's defects responsibility and which are the immediate responsibility of specialist ecologists or land managers. Contractors must remain alert to any defects that may relate to their design and ensure that they can respond promptly to possible adverse BNG monitoring or reporting outcomes which may arise for the client.
Biodiversity net gain requirements now apply to nationally significant infrastructure projects, marking a major shift for large-scale infrastructure developments. In this article, we explore what the new requirements mean in practice and the challenges they present for developers, contractors and consultants in relation to project delivery, risk allocation and ongoing habitat maintenance obligations in particular.