Biodiversity Net Gain: Three Key Policy Updates

On 15 April 2026, the Department for Environment, Food & Rural Affairs (Defra) published three policy updates representing a significant reshaping of the biodiversity net gain (BNG) regime in England. Since becoming mandatory in 2024, BNG – which requires most new development in England to deliver at least a 10% biodiversity uplift maintained for 30 years – has become a central consideration for development design and viability. These latest reforms represent a dramatic evolution of the framework.

In summary, Defra has:

• Confirmed that mandatory BNG will apply to nationally significant infrastructure projects (NSIPs) from 2 November 2026;
• Introduced new exemptions for smaller developments, including all development on sites of 0.2 hectares or less; and
• Launched a public consultation on whether brownfield residential schemes should be exempted from BNG requirements.

We explain each of these changes below and set out what they mean in practice.

Mandatory BNG for NSIPs

The Environment Act 2021 established the statutory basis for extending mandatory BNG to NSIPs, which includes major transport, energy and water schemes. Although this extension was originally expected to take effect from May 2026, the Government has now confirmed that mandatory BNG will apply to all NSIP applications submitted on or after 2 November 2026.

The key confirmed elements of the NSIP BNG regime include:

• A uniform 10% net gain requirement across all sectors: Defra has opted against sector-specific exemptions and will apply the same 10% BNG requirement on all NSIP types.
• Targeted BNG boundaries: BNG will not be assessed across the full red line boundary of an NSIP. Instead, it will apply only to habitats that are negatively impacted by the development (whether temporarily or permanently) or to habitats within the order limits that are used to contribute towards BNG. Habitats that are unaffected by the underlying infrastructure project will be excluded from baseline assessments, addressing long‑standing proportionality and cost concerns.
• Flexible delivery routes: NSIP promoters will be able to rely on both on‑site and off‑site delivery as their primary means of achieving BNG, with statutory biodiversity credits remaining a last resort. Off‑site biodiversity units may be sourced from any local planning authority (LPA), National Character Area (NCA) or Marine Plan Area which the NSIP BNG boundary falls within without attracting a spatial risk multiplier penalty.
• Temporarily affected habitats: any new or enhanced habitats created on‑site and counted towards a scheme’s biodiversity score will be treated as “significant” habitats for the purposes of the BNG regime. These habitats must be maintained for 30 years and secured through a legal agreement, such as a requirement in a Development Consent Order (DCO), a planning obligation or a conservation covenant. By contrast, habitats that are temporarily impacted and then reinstated back to its pre-development condition, are considered "non-significant" for BNG purposes. Such habitats can be included in calculations to contribute to BNG but do not have to be secured through a legal agreement.
• Biodiversity gain plan: NSIP promoters will be required to submit a biodiversity gain plan alongside their DCO application. This will set out the proposed approach to achieving 10% BNG, identify the role of suitably qualified ecologists, and include the completed biodiversity metric calculation.

Defra intends to lay the relevant secondary legislation and publish updated biodiversity gain statements aligned with National Policy Statements in May 2026, together with further guidance ahead of the November go‑live date. NSIP applications submitted before 2 November 2026 will not be subject to the new requirements.

BNG exemptions for smaller developments

Alongside the NSIP announcement, Defra has confirmed a package of reforms relating to minor, medium and brownfield development. These measures are intended to reduce the disproportionate cost and administrative burden that mandatory BNG has placed on smaller schemes.

The key reforms include:

• A new 0.2 hectare area-based exemption: the most significant change is that all development where the site is area within the red line boundary is 0.2 hectares or less will be fully exempt from BNG. Defra estimates this will remove BNG requirements from around half of residential planning permissions that were previously in scope. The exemption will not apply where priority habitats are affected – these being habitats of principal importance for conserving or enhancing biodiversity, as published on Natural England's website.
• Removal of self-build and custom build exemption: the existing exemption for small scale self-build and custom build development will be removed. In practice, however, many such projects are likely to be captured by the new 0.2 hectare exemption instead.
• New targeted exemptions: further exemptions will be introduced for developments whose primary objective is to conserve or enhance biodiversity; temporary planning permissions granted for a maximum of five years (unless on-site priority habitats are affected); and developments enhancing parks, playing fields and public gardens.
• Increased flexibility for minor developments: for minor developments only, including residential developments with nine or fewer dwellings on a site of one hectare or less, off-site biodiversity delivery will be given equal status with on-site delivery, loosening the existing biodiversity gain hierarchy, making it easier for developers to find a BNG solution.
• Spatial risk multiplier reform: for all development types, the spatial risk multiplier will soon be assessed based on Local Nature Recovery Strategy (LNRS) areas rather than LPA and NCA boundaries. With only 48 LNRS areas currently designated across England (compared to 337 LPAs), this reform significantly expands the pool of off‑site biodiversity units that can be used without attracting a multiplier penalty.

Secondary legislation to introduce the 0.2 hectare exemption, remove the self‑build exemption, exempt temporary planning permissions (up to five years), and amend the biodiversity gain hierarchy for minor development is expected to come into force before 31 July 2026, with the remaining measures implemented in stages later in the year.

Brownfield residential exemption: consultation now open

Defra has also launched a consultation on whether residential brownfield development should benefit from a targeted exemption from BNG requirements.

The consultation, which closes on 10 June 2026, contends that delivering BNG on brownfield land can be more complex, and proportionately more costly, than on greenfield sites. Defra is seeking views on:

• The case for a targeted brownfield residential exemption: whether predominantly residential brownfield schemes should be exempt from BNG, in addition to the confirmed exemption for sites below 0.2 hectares. Commercial‑led or mixed‑use schemes with only a minor residential element would remain subject to BNG.
• Definition of "brownfield residential development": how “brownfield residential development” should be defined for regulatory purposes, including a proposed requirement that at least 75% of the application site comprises Previously Developed Land, linked to the existence of a lawful permanent building or structure dating from 1948 onwards.
• Appropriate size thresholds: potential site‑area thresholds of 0.5, 1, 1.5, 2 or 2.5 hectares, reflecting a policy intention to focus on urban sites rather than rural schemes which may be larger.
• Environmental safeguards: how ecological impacts should be constrained, including confirmation that any exemption would not apply where priority habitats are affected and whether additional protections for valuable urban habitats are needed.
• Wider impacts on the BNG system: the effects of a brownfield exemption on housing delivery, biodiversity outcomes and the operation of the off‑site BNG market, as well as any unintended behavioural consequences.

What this means for developers

The key practical takeaways are:

• For NSIP promoters and developers: the 2 November 2026 go‑live date provides promoters, who were expecting BNG to apply from May, an extended period for preparation, albeit with more visibility on the detail which was otherwise still awaited. BNG will need to be fully embedded in project design, with biodiversity gain plans and input from qualified ecologists being prepared well in advance of submission.
• For SME developers and housebuilders: the new 0.2 hectare exemption should provide relief for many smaller schemes once it comes into force this summer. Where BNG still applies, the relaxed biodiversity gain hierarchy should make off‑site delivery more straightforward.
• For landowners and habitat providers: the reforms are likely to have mixed effects on the off-site BNG market. While Defra expects the new exemptions will reduce demand for off‑site biodiversity units by around 10%, the extension of mandatory BNG to NSIPs and the reform of the spatial risk multiplier are likely to generate new demand, particularly for certain habitat types and locations.

Taken together, these announcements signal a more differentiated approach to BNG, rather than a 'one-size-fits-all' for all development types. There is clearly a commitment to evolving regulation in order to ensure that development can continue – in particular for the benefit of housebuilders. We continue to monitor these develops and await to see whether the emerging natural capital sector (landowners and habitat banks in particular) may need to adapt further as the changes come into effect and the policy evolves, which may impact the speed of landscape-scale nature restoration and conservation.

On 6 May 2026, join our webinar Delivering nature at scale: BNG for major infrastructure projects, where our specialists will unpack these reforms and what the new NSIPs BNG regime means in practice.

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