Biodiversity Net Gain (BNG), once a visionary concept within the Environment Act 2021, has quickly become a practical obligation for developers across England. As of June 2025, all but the smallest residential and commercial schemes must now deliver at least a 10% improvement in biodiversity on, or associated with, their sites, whether through on-site habitat creation, off-site investment, or, in limited cases, the purchase of statutory biodiversity credits. But as the first wave of mandatory implementation unfolds, practical concerns are surfacing, particularly from small to mid-size developers, and it seems that the government is listening.
In May 2025, Defra launched two parallel consultations. The first proposes wide-ranging adjustments to how Biodiversity Net Gain operates for minor and medium-scale development, especially on brownfield land. The second focuses on how BNG might be integrated into the consent regime for Nationally Significant Infrastructure Projects (NSIPs) from 2026. While these consultations reflect different scales of development, they share a common purpose: making BNG more proportionate, more navigable, and more effective.
This article outlines how Biodiversity Net Gain currently functions in law, unpacks the key proposals in each consultation, and explores what they might mean in practice, particularly for rural landowners, developers, and infrastructure promoters who are considering how best to engage in shaping the evolving regulatory landscape.
Biodiversity Net Gain as it stands
Under the Environment Act 2021, any development falling within the Town and Country Planning Act 1990 is required to leave biodiversity in a measurably better state than it was pre-development. This means achieving a net gain of at least 10% in biodiversity value, as measured by a statutory metric. Developers must first seek to deliver gains on-site, and if this proves impractical, they may turn to the growing off-site market or, as a last resort, purchase biodiversity credits from government.
For larger developments, BNG has been mandatory since February 2024. Smaller developments (residential schemes of fewer than 10 dwellings, for example) have been subject to Biodiversity Net Gain since April 2024. To ease the burden on these smaller schemes, a simplified “small sites metric” (SSM) was introduced, allowing developers without access to ecological consultants to calculate their net gain using standardised habitat values.
As the system settles into practice, feedback from developers, local authorities, and environmental groups has revealed a mixed picture. While BNG is broadly functioning as intended for larger schemes, smaller projects, especially those on constrained or previously developed land, are struggling to deliver gains cost-effectively. Many are reliant on fractional unit purchases in an emerging, and still fragmented, off-site market.
Government signals a willingness to adapt
Responding to these early implementation challenges, Defra’s new consultation for minor, medium, and brownfield development proposes an overhaul of key aspects of the BNG regime. Running until 24 July 2025, the consultation explores three main themes: exemption reform, metric simplification, and greater off-site flexibility.
1. Rethinking exemptions
The government is considering whether the current list of exemptions goes far enough in shielding genuinely low-impact development. Among the options under review:
- A blanket exemption for all minor development, including small residential schemes up to 9 dwellings. This would remove the Biodiversity Net Gain requirement entirely for a large swathe of planning applications.
- Raising the “de minimis” threshold, which currently exempts developments that disturb less than 25 square metres of habitat. Proposed thresholds range up to 250 square metres.
- Replacing the somewhat unworkable exemption for self and custom build schemes with a simpler exemption for any single dwelling on a plot under 0.1 hectares, provided no priority habitats are affected.
Other new exemption categories are also mooted, including for development on playing fields (where impacts are confined to low-value grassland), for genuinely temporary development under five years, and for conservation projects whose primary purpose is ecological enhancement.
2. Reforming the small sites metric
The small sites metric (SSM) was designed to make Biodiversity Net Gain accessible to small developers, but practical use has revealed several flaws. Key proposals include:
- Allowing the SSM to be used for “medium” developments, potentially those up to 49 dwellings, where the site is under 1 hectare and contains no priority habitat.
- Removing or relaxing “trading rules” that currently require certain habitat types to be replaced like-for-like.
- Fixing the baseline habitat condition at “poor” rather than “moderate,” to avoid unfairly penalising developments on degraded land.
- Merging habitat types within the SSM to simplify classification and open the door for AI-driven image analysis tools to assist with assessments.
If taken forward, these changes could make the BNG process more intuitive for smaller developers and reduce reliance on costly off-site units.
3. More flexibility to go off-site
For minor developments where on-site biodiversity gain is simply unfeasible, whether due to scale, layout constraints or existing site conditions, developers are often left sourcing tiny fractions of habitat units. These are not only expensive to procure but difficult to secure contractually.
Defra is therefore considering changes to the biodiversity gain hierarchy for minor development. These might allow developers to bypass the preference for on-site delivery, instead defaulting directly to registered off-site sites or credits. The aim is to reduce transactional burdens without undermining the overall BNG objective.
Biodiversity Net Gain for Nationally Significant Infrastructure Projects
While small-scale developers seek relief, the infrastructure sector is preparing to be brought into the Biodiversity Net Gain fold for the first time. Defra’s second consultation, which also closes in July, sets out the proposed practical application of BNG to NSIPs from May 2026.
The proposals suggest a consistent national framework, requiring all onshore Nationally Significant Infrastructure Projects (from energy and transport to water and waste) to meet the 10% Biodiversity Net Gain threshold. However, unlike ordinary developments, NSIPs will not be required to prioritise on-site gains, a move designed to avoid incentivising the compulsory acquisition of land purely for BNG purposes. Instead, applicants can deliver their gains off-site or by purchasing statutory credits from day one.
The consultation also proposes bespoke rules for calculating Biodiversity Net Gain on large linear schemes, dealing with temporary land take during construction, and ensuring biodiversity enhancements do not conflict with aerodrome safeguarding or other safety regulations.
NSIP promoters will need to submit a Biodiversity Gain Plan as part of their Development Consent Order (DCO) application, and potentially phase that delivery over time. This could add a new dimension to project consenting and land strategy at a time when many schemes are already navigating significant environmental obligations.
What does all this mean in practice?
For rural landowners and developers, these consultations signal two things clearly.
First, Biodiversity Net Gain is here to stay. There is no suggestion that the requirement will be rolled back or weakened, only that it should be made more workable, particularly at the margins of the planning system.
Second, there is a real opportunity now to help shape what that workability looks like. Both consultations are open to public response until 24 July 2025. For those involved in small site delivery, rural housing, brownfield regeneration, or infrastructure development, this is a critical moment to inform the direction of policy.
While the consultations have been welcomed by many smaller developers and planning authorities keen to reduce cost and complexity, the response elsewhere has been more cautious.
Critics argue that exempting minor development risks undermining the intent of BNG entirely, pointing out that such sites make up the majority of planning applications and a substantial proportion of transactions in the emerging biodiversity units market. Environmental groups have warned that the proposed changes could weaken one of the government’s few enforceable commitments to nature recovery. Others are worried that the changes would unintentionally encourage the fragmentation of bigger plans in order to completely circumvent BNG commitments.
Because of this, at Buckles Solicitors, we are encouraging our clients to engage proactively with the consultation process. Whether your interest lies in securing Biodiversity Net Gain exemptions, clarifying your responsibilities as a promoter, or leveraging the off-site Biodiversity Net Gain market as a landowner, now is the time to make your voice heard.
Final thoughts
Biodiversity Net Gain represents a profound change in how we think about land, planning, and development. It seeks not just to offset harm, but to actively improve the state of nature in and around the places we build. But as with any new regime, the devil is in the detail, and the balance between environmental ambition and practical delivery is still being struck.
For advice on navigating the current BNG rules or contributing to the Defra consultation, please get in touch with our Agricultural & Rural Affairs team.
