As England continues its transition toward more sustainable patterns of growth, Biodiversity Net Gain (BNG) has emerged as one of the most ambitious environmental policies to enter the planning system in recent years. Its purpose is simple and well-intentioned to ensure that development leaves the natural environment in a measurably better state than before.
The principle is widely supported across the planning and environmental sectors. However, as we heard at our recent Bell Cornwell Roundtable, where planners, ecologists, architects and local authority officers came together to discuss the realities of implementation, the execution of BNG is proving very far from straightforward.
A Good Idea in Principle
There is no question that the policy has encouraged earlier collaboration between planners, ecologists and designers, helping to shape more environmentally conscious proposals. In some cases, BNG has led to creative solutions – re-purposing open space, integrating green infrastructure, and designing developments that actively support local habitats and community wellbeing.
When applied proportionately and flexibly, BNG adds value to design quality and placemaking – outcomes everyone in the planning process can support.
Flaws in Execution
However, feedback from the Roundtable highlighted that inconsistent interpretation, rising costs and procedural complexity are undermining the principle and impeding the delivery of much needed growth.
Across local authorities, the way BNG requirements are applied varies significantly. While national guidance suggests that BNG should be secured through planning conditions after permission, many councils now require full biodiversity metrics and management plans before validation, even for minor schemes.
This approach is creating unnecessary delay and additional cost, particularly for small and medium-sized developers who may lack the resources to prepare detailed ecological assessments at an early stage. In some instances, off-site BNG credits are the only viable option, but the costs can be prohibitive, sometimes exceeding the development value of the site itself.
Participants also noted that BNG credits are often purchased miles away from the affected community, weakening the connection between local development and local environmental benefit. The result is a process that risks becoming more about administration than outcomes.
A Need for Proportion and Clarity
What came through strongly from our discussion was that BNG can work, but only with clear, consistent and proportionate application. Developers and local planning authorities alike need greater certainty about what is required, when, and at what stage.
A more pragmatic approach could involve:
- Applying the policy proportionately to the scale and type of development;
- Securing BNG by condition rather than front-loading requirements;
- Ensuring off-site mitigation remains locally relevant; and
- Providing consistent training and guidance for local planning officers.
BNG as Part of the Solution
At its heart, Biodiversity Net Gain is a good idea – one that recognises the vital role planning plays in tackling environmental decline. But as our Roundtable revealed, poorly aligned policy and inconsistent implementation risk turning a good idea into a flawed process.
BNG should be an opportunity to bring together ecology, design, and development in pursuit of better outcomes for people and nature. With greater clarity and balance, it still can be.
“BNG has become front-loaded and bureaucratic. It was meant to be dealt with by condition, but councils now demand full metrics before validation. It’s turned into an expensive legal exercise.”
Nick Cobbold, Partner, Bell Cornwell LLP
