18 December 2025
The pioneering Biodiversity Net Gain (BNG) legislation that was introduced in England in early 2024, mandating a 10% gain for biodiversity in the majority of new developments, is set to be watered down by the UK government.
BNG is a world-leading mechanism for conserving and restoring nature and offsetting biodiversity losses across both major and small-scale development, currently excluding Nationally Significant Infrastructure Projects (NSIPs).
The approach puts an onus on developers to quantify any biodiversity losses during construction and compensating for any nature losses by funding an equal amount of habitat restoration plus at least an additional 10% - preferably onsite or at an alternative location.
Ahead of proposed changes to England’s National Planning Policy Framework due in early 2026 to speed up the building of new homes and infrastructure, the UK Government has announced proposals for BNG to be watered down.
Early indications were that small site developments under one hectare (2.5 acres or 10,117 sq m) would be exempt from undertaking BNG, while reports in recent weeks suggested a 0.5 hectare exemption was planned. What emerged were proposals that developments under 0.2 hectares (2000 square metres) would be exempt from BNG rules, with additional targeted exemptions for brownfield housing sites. This is signficantly larger than the current 25 square metres.
The Government also announced plans to consult on requirements for new developments to include low-cost “swift bricks” wherever possible, to create thousands of nesting opportunities for the migratory birds which have seen numbers decline 60% since the mid-1990s. Swift-bricks are currently mandatory in new developments in The Netherlands.
Responding to the publication of the proposed NPPF changes and signals to BNG reform, Lesley Wilson, Policy and Engagement Lead for Biodiversity and Natural Capital at ISEP, said: “It is essential that the UK Government seeks to deliver infrastructure and housing alongside nature restoration, so that the UK has the housing and infrastructure it needs with thriving local communities and resilient ecosystems services that support food, water, climate mitigation and adaptation.
“Aligning the planning system in a way that supports the Government’s nature targets through the National Planning Policy Framework will be an important step towards realising this vision.
“The inclusion of nature-friendly measures such as swift bricks in the framework is welcome, as is the recognition of considering environmental opportunities and safeguards at the planning stages.
“However, the exemptions trailed by the government for biodiversity net gain (BNG) need to be carefully considered.
“Increasing the threshold for BNG on small sites from 25 square metres to 2000 square metres, is disappointing – increasing impacts on nature and likely reducing nature corridors – though not as damaging as initially proposed.
Biodiversity Net Gain is measured using the Biodiversity Metric – developed by Natural England in the UK – and is gaining attention worldwide, including being referenced at the last United Nations Biodiversity Conference (COP16) in Cali, Colombia.
The biodiversity metric provides a robust and risk-based mechanism for quantifying habitat change in different scenarios in a way that developers and landowners of differing scales can use to understand and address how they could provide benefits for nature.
Its flexible framework allows it to be adapted to different contexts and ecosystems, enabling global stakeholders to measure biodiversity impacts consistently and transparently. The metric aids communication between ecologists and decision makers and drives positive biodiversity outcomes, ensuring that development and nature can thrive together.
It is helping countries around the globe adopt a measurable, transparent approach to biodiversity restoration. It is playing an increasing role in global efforts to create, protect, and enhance biodiversity, helping to restore nature worldwide.
The biodiversity metric is not only being utilised across England for Biodiversity Net Gain (BNG) but has also found applications across the globe, with variants now in use in places as diverse as Saudia Arabia, the US, the Netherlands and India. Organisations from America to Sweden to Oman have adapted and adopted the biodiversity metric, reflecting its international significance.
One notable example of the biodiversity metric's international reach is in Sweden. Uppsala, the country’s fourth-largest municipality, has developed a program to offset negative impacts on biodiversity resulting from urban growth.
Political leaders approved a set of principles for biodiversity offsetting in June 2024, with the requirement to offset expected to be in place in 2025.
Created by Natural England
