Understanding the “10% Biodiversity Gain” in the Proposed Blundel Lane Development

As the proposed housing development at Blundel Lane, Stoke d’Abernon, Surrey moves forward, developers will be required to demonstrate a 10% biodiversity gain as part of their planning obligations. This concept, introduced under the Environment Act 2021, aims to ensure that developments leave the natural environment in a measurably better state than before.

However, while a biodiversity net gain (BNG) of 10% may sound positive, there are important limitations, challenges, and potential downsides that residents should be aware of. This article explores what BNG means, how it is measured, and why it may not always deliver the environmental benefits promised.

What Is a 10% Biodiversity Net Gain (BNG)?

Biodiversity Net Gain (BNG) is a planning policy requirement designed to compensate for the environmental impact of new developments. Under this policy:

• Developers must assess the existing biodiversity value of a site before construction.

• They are required to enhance biodiversity by at least 10%, either on-site or through off-site compensatory measures.

• This is measured using a biodiversity metric developed by Natural England, which assigns a numerical value to habitats based on their ecological importance.

• BNG must be maintained for at least 30 years, but monitoring and enforcement are often limited.

How Developers Achieve a 10% Biodiversity Gain

To meet the BNG requirement, developers use a combination of the following strategies:

1. On-Site Habitat Enhancements

   • Planting new trees and hedgerows.

   • Creating wildflower meadows and green corridors.

   • Installing ponds or wetland areas for wildlife.

2. Off-Site Biodiversity Offsetting

   • If developers cannot achieve BNG on-site, they can pay for biodiversity improvements elsewhere, sometimes far from the affected community.

   • Landowners and conservation groups can sell biodiversity credits, meaning developers do not have to improve biodiversity locally.

3. Biodiversity Credits

   • Developers may purchase biodiversity credits from the UK government to meet their obligations without making direct habitat improvements.

While these strategies can support ecological recovery in principle, they come with several key risks and limitations.

Potential Downsides and Concerns About the 10% Biodiversity Gain Requirement

1. Loss of Established Habitats and Mature Trees

• Many development sites, including Blundel Lane near Polyapes Scout Site, contain mature trees, hedgerows, and long-established ecosystems.

• Even if new trees are planted, it takes decades for them to provide the same biodiversity benefits as an established woodland or hedgerow.

• Developers often clear habitats first and then claim “biodiversity gain” by replanting in different areas. This is not a genuine gain—it’s a net loss.

💡 Key concern for residents: Will the existing ancient trees, hedgerows, and green spaces be protected, or will they be cleared and replaced with less valuable ‘new’ habitats?

2. Poor Quality and Tokenistic Green Spaces

• Some developers prioritize quantity over quality, creating small, fragmented green areas that are of low ecological value.

• A patch of grass with a few trees is not the same as a thriving natural ecosystem, yet it may still count towards BNG targets.

• Developers sometimes include green roofs or planted flowerbeds, which do not provide the same biodiversity benefits as natural habitats.

💡 Key concern for residents: Will the new habitats be ecologically valuable, or are they just meeting a target on paper?

3. Off-Site Compensation Weakens Local Biodiversity

• If developers cannot meet the 10% gain on-site, they can pay for biodiversity improvements elsewhere.

• This could mean that biodiversity is lost in Stoke d’Abernon, but compensated for in a completely different area.

• Biodiversity should be improved where the damage occurs, not displaced elsewhere.

💡 Key concern for residents: Will biodiversity gains be delivered locally, or will they be offset miles away with no benefit to the community?

4. Biodiversity Gains Are Not Always Permanent

• While developers must commit to maintaining BNG for 30 years, enforcement is weak.

• Once planning permission is granted, future landowners or management companies may not properly maintain the green spaces.

• In some cases, biodiversity-rich areas are later repurposed for further development once the initial focus on planning approval fades.

💡 Key concern for residents: Who will monitor and enforce biodiversity gains over the long term? Will there be penalties if habitats decline over time?

5. Increased Housing Density to Accommodate Green Spaces

• To meet BNG targets within a development, developers may increase housing density by building more compact homes to free up space for green areas.

• This can lead to:

  • Overcrowding with less space between homes.

  • Traffic congestion due to more houses being built than originally planned.

  • Pressure on local services (schools, GP surgeries, transport).

💡 Key concern for residents: Will the inclusion of green spaces result in higher housing density elsewhere, causing strain on local infrastructure?

6. The Risk of “Biodiversity Washing”

• BNG can be manipulated to make a development seem more environmentally friendly than it actually is.

• Developers promote biodiversity gains in marketing materials, even if the reality is much less effective.

• Some developers clear valuable habitats before baseline biodiversity assessments, so they start from a lower point and can claim gains more easily.

💡 Key concern for residents: Will the biodiversity assessments be independent and transparent, or will developers manipulate the figures?

What Can Residents Do?

To ensure that the 10% biodiversity gain is meaningful and not just a box-ticking exercise, residents should:

1. Scrutinize the Planning Application

   • What habitats will be lost?

   • Are biodiversity gains happening on-site or elsewhere?

   • What long-term management plans are in place?

2. Challenge the Quality of BNG Measures

   • Are the proposed green spaces genuinely beneficial for biodiversity, or are they just token landscaping?

   • Will the new habitats be connected to existing wildlife corridors?

3. Push for Transparency and Accountability

   • Request independent ecological assessments rather than relying on developer-funded reports.

   • Ensure that BNG is monitored over time, with clear consequences if targets are not met.

4. Engage with Local Authorities and Environmental Groups

   • Work with local councillors and wildlife organizations to ensure BNG is properly implemented.

   • Raise concerns during public consultations.

Conclusion

While the 10% biodiversity net gain policy has the potential to protect and enhance natural habitats, it is not always implemented effectively. For Stoke d’Abernon, it is essential that BNG commitments are genuine, well-planned, and properly enforced—not just a tool for developers to push through damaging proposals.

By staying informed, engaged, and proactive, local residents can hold developers accountable and help ensure that biodiversity gains truly benefit the community and local environment—not just exist on paper.