Biodiversity Net Gain: mandatory BNG for NSIPs confirmed as government unveils significant reforms
On 15 April 2026, the Government confirmed that biodiversity net gain (“BNG”) will become mandatory for all nationally significant infrastructure projects (“NSIPs”) from 2 November 2026, opting not to introduce sector-specific exemptions or voluntary approaches. The confirmation came as part of the Government's response to its 2025 consultation on BNG for NSIPs, published alongside a response to a parallel consultation on minor, medium and brownfield development and the launch of a new consultation on a potential targeted exemption for residential brownfield sites.
BNG for NSIPs
Mandatory from 2 November 2026
The headline announcement from the NSIP consultation response is the confirmation that BNG will become mandatory for all English onshore NSIP applications submitted on or after 2 November 2026.
The Government has opted not to introduce sector-specific exemptions or voluntary approaches, applying a consistent 10% BNG requirement across all NSIP types. This was supported by the majority of consultation respondents, who emphasised the importance of consistency and accountability for biodiversity impacts across all infrastructure sectors.
An RSPB campaign called for a higher biodiversity gain objective for major infrastructure projects, arguing that the current metric would not deliver nature recovery at a scale matching the impact of NSIPs. However, Defra has decided to retain the biodiversity gain objective at 10%, maintaining alignment with the Town and Country Planning Act 1990 (“TCPA”) regime to ensure consistency and provide certainty for developers and stakeholders.
BNG Boundary: A Narrower Baseline
Another significant announcement relates to which habitats must be included in the BNG baseline (the pre-development biodiversity value of a site, against which the 10% net gain requirement is measured). While 60% of respondents supported applying BNG to the entire geographic boundaries defining the full extent of powers sought through a development consent order (“DCO”)), a large majority of developers did not, arguing that such DCO limits are often drawn much wider than the area actually impacted.
In response, the Government has decided that unimpacted habitats do not need to be included in the BNG baseline. Instead, the 10% BNG requirement will apply to a smaller area referred to as the "BNG boundary", which includes habitats within the DCO limits that are negatively impacted by the development, together with habitats (within the DCO limits) that are used to contribute towards BNG. This approach will be welcome, and is intended to balance ambitious biodiversity outcomes with proportionate requirements, and to maintain incentives for applicants to minimise construction impacts since unimpacted areas are excluded from the baseline by default. Applicants will be required to provide a BNG boundary plan as part of their outline biodiversity gain plan, identifying all areas of habitat included in the baseline.
Delivering BNG: On-site or Off-site in the First Instance
A significant departure from the TCPA regime is the approach to on-site versus off-site delivery. It has been confirmed that for NSIPs, developers will be able to deliver on-site or off-site gains in the first instance, as suits the particular development need. There will be no requirement to try to deliver gains on-site before going down the off-site route. Statutory biodiversity credits remain available only as a last resort. The rationale is that the scale of NSIPs creates the potential to produce better ecological outcomes through strategic delivery that may involve off-site gains.
Significant versus Non-significant Gains
The Government has introduced an important distinction between "significant" and "non-significant" on-site gains. All habitat creation and enhancement counted towards the post-development biodiversity value is considered significant and must be legally secured for at least 30 years. By contrast, reinstatement of existing habitats – that is, replacing a temporary loss with the same habitat type and condition – is considered non-significant and does not need to be secured. This is intended to alleviate concerns over the practical difficulty of securing gains on land acquired temporarily and typically returned to its previous owner after construction.
The BNG metric user guide will also be updated to reflect the fact that NSIPs typically have longer timescales for temporary impacts than TCPA development. The existing rule allowing habitats that are temporarily impacted and restored within two years to be counted as retained will be extended to five years for habitats of low and very low distinctiveness in the NSIP context.
Biodiversity Gain Plans
The Government has adopted a phased approach to biodiversity gain plans for NSIPs. Applicants must submit an outline biodiversity gain plan at the application stage which must set out the overall strategy for meeting the 10% BNG objective. An updated or phase biodiversity gain plan must then be submitted for approval prior to commencement of development of each phase of development. Any final shortfall in gains must be calculated and secured before the operation of the project at the latest.
The Government has also introduced flexibility in who can act as the discharging authority for post-consent biodiversity gain plans. This role may be fulfilled by a relevant planning authority, such as the host local planning authority or a lead local planning authority for projects spanning multiple authorities, or alternatively by the Secretary of State in consultation with relevant planning authorities.
In response to stakeholder feedback, the Government will require applicants to confirm within their biodiversity gain plan how qualified ecologists have contributed to the development of the plan, the metric calculation, and the habitat management and monitoring proposals.
Wider BNG Reforms
Alongside the NSIP consultation response, the Government published its response to the parallel consultation on improving BNG implementation for minor, medium and brownfield development. The Government has also launched a new eight-week consultation exploring a further targeted exemption from BNG for some brownfield residential development, closing on 10 June 2026.
Confirmed Changes for Minor and Medium Development
There is to be a new area-based exemption for all development where the site area within the red line boundary is 0.2 hectares or below, which the Government estimates will exempt around 50% of residential planning permissions previously required to deliver BNG. The exemption will not apply where on-site priority habitats are impacted.
Further targeted exemptions have been confirmed for development whose primary objective is to conserve or enhance biodiversity, temporary planning permissions of five years or less, and development enhancing parks, playing fields and public gardens where no on-site priority habitats are impacted. The biodiversity gain hierarchy will also be amended for minor development only, placing off-site biodiversity gains on the same preference level as enhancement and creation of on-site habitat (as with the NSIP regime), making it easier for smaller developers to access the off-site market.
New Consultation: Residential Brownfield Exemption
The new consultation arises from the Government's brownfield-first approach to housing delivery and explores whether BNG should be disapplied for certain residential brownfield development. It proposes a regulatory definition under which "brownfield development" would mean development where at least 75% of the land within the planning application boundary is "previously developed land”.
The consultation seeks views on a range of area-based thresholds (ranging from 0.5 to 2.5 hectares) which would operate in addition to the above-mentioned 0.2 hectare exemption. Under the higher thresholds, modelling suggests that up to 64% of currently non-exempt residential planning applications could become exempt when considered alongside the 0.2 hectare exemption. The combined impact of the 0.2 hectare and proposed brownfield exemption could lead to more than one‑fifth of biodiversity units currently delivered through BNG being foregone.
Practical Implications and Next Steps
For NSIPs, the Government’s response provides long-sought certainty on the scope and process for mandatory BNG, and some elements, such as the narrower BNG boundary and the flexibility on temporary land use, will be welcomed by developers. Priority guidance on these changes will be published “early in 2026”, and Defra will lay statutory instruments and publish biodiversity gain statements for all NSIP types in May 2026.
For smaller developers, the 0.2 hectare exemption and changes to the biodiversity gain hierarchy represent a tangible reduction in administrative and cost burdens, although these changes also bring implications for the off-site BNG market (and the outcome of the new brownfield residential consultation could amplify these market effects further). Roisin Laycock comments that “any impact on the off-site BNG market resulting from a reduction in demand from minor development and brownfield residential development should be mitigated by the introduction of mandatory BNG for NSIPs, though the extent of such mitigation remains unclear”. Subject to parliamentary scheduling, the changes are set to come into force by 31 July 2026, with Defra bringing forward secondary legislation before the summer recess.
Co-authored by Ollie Mather, trainee solicitor at CMS.
