Biodiversity Net Gain – Frequently Asked Questions

Biodiversity net gain (BNG) is now a central part of the planning system in England, requiring most developments to leave biodiversity in a measurably better state than it was before development. Below, we answer some of the most common FAQs for developers and landowners

What is Biodiversity Net Gain?

Biodiversity net gain is a legal requirement that most new developments must deliver at least a 10% increase in biodiversity compared to the site’s pre-development baseline. The requirement is set out in Schedule 7A of the Town and Country Planning Act 1990, introduced by the Environment Act 2021.

In simple terms, before a development site is built on, its existing habitats are assessed using the statutory biodiversity metric. After development, the completed scheme must demonstrate that biodiversity value has increased by at least 10%, either on-site, off-site, or via statutory biodiversity credits (as a last resort).

What is the BNG requirement?

The BNG requirement applies to most developments requiring planning permission in England. Developers must submit biodiversity gain plans demonstrating how a minimum 10% net gain will be achieved and maintained for at least 30 years.

The biodiversity gain must be:

• Calculated using the statutory biodiversity metric
• Secured through planning conditions or a legal agreement
• Maintained for at least 30 years
• Recorded on the Biodiversity Gain Site Register (for off-site units)

Does BNG apply to all planning applications? 

BNG applies to most planning applications submitted under the Town and Country Planning regime. However, there are some exemptions and transitional arrangements.

BNG applies to:

• Major developments
• Small sites (subject to modified requirements)
• Nationally significant infrastructure projects (with separate implementation provisions)

Certain developments are exempt, such as:

• Permitted development
• Householder applications
• Some urgent Crown developments
• Development impacting very small areas of habitat (below de minimis thresholds)

It is always important to confirm whether your project is captured at the earliest stage of the planning process.

How are small sites treated under BNG?

Small sites benefit from a simplified version of the statutory biodiversity metric. This is intended to reduce cost and complexity for smaller developers while still delivering measurable biodiversity improvements.

Although the calculation process may be streamlined, small sites must still meet the 10% net gain target and comply with the same requirement that biodiversity enhancements are maintained for at least 30 years.

What are biodiversity gain plans?

Biodiversity gain plans are documents submitted to the local planning authority for approval before development begins. They demonstrate how the required 10% biodiversity uplift will be achieved.

A biodiversity gain plan typically includes:

• The pre-development biodiversity value
• The post development biodiversity value
• Details of habitats types created or enhanced
• Whether gain is delivered on-site, off-site, or via statutory credits
• How habitats will be secured and managed

Planning permission cannot be lawfully implemented until the biodiversity gain plan has been approved.

What is the statutory biodiversity metric?

The statutory biodiversity metric is a calculation tool published by Natural England. It measures biodiversity in “biodiversity units” based on:

• Habitat type
• Habitat condition
• Distinctiveness
• Strategic significance
• Size (area or length)

This standardised approach ensures that biodiversity losses and gains are assessed consistently.

What does strategic significance mean?

Strategic significance refers to whether a habitat is located in an area identified as important for nature recovery. This is typically determined by reference to the Local Nature Recovery Strategy (LNRS).

If habitat creation or enhancement aligns with the priorities identified in a Local Nature Recovery Strategy LNRS, it may score higher within the metric. This encourages developers and land managers to deliver biodiversity where it will have the greatest ecological impact.

What habitat types can count towards net gain?

A wide range of habitat types can contribute to biodiversity net gain, including:

• Grasslands
• Woodlands
• Wetlands
• Hedgerows
• Rivers and streams
• Urban habitats

The statutory biodiversity metric classifies habitat types according to their distinctiveness and condition. Higher distinctiveness habitats typically generate more biodiversity units but may also carry greater delivery and management risk.

What happens if net gain cannot be achieved on the development site?

If the required uplift cannot be delivered entirely on the development site, developers can:

• Deliver off-site biodiversity gains on other land
• Purchase biodiversity units from a third-party land manager
• Purchase statutory biodiversity credits from the government (as a last resort)

Off-site biodiversity must be legally secured and registered. The land must be maintained for at least 30 years and subject to a legal agreement or conservation covenant.

What is a conservation covenant?

A conservation covenant is a private, voluntary legal agreement between a landowner and a designated responsible body (such as a conservation organisation or public authority).

It ensures that land is managed in a specified way for conservation purposes and binds successors in title. A conservation covenant is one way to secure off-site biodiversity gain.

The agreement must be for a minimum term of 30 years, ensuring biodiversity enhancements are maintained for at least 30 years.

What is a Section 106 Agreement in the context of BNG?

A Section 106 Agreement is a legal agreement entered into under the Town and Country Planning Act 1990 between a developer and the local planning authority.

For biodiversity net gain, a Section 106 Agreement can:

• Secure habitat creation and management obligations
• Ensure monitoring and reporting
• Restrict development until gain is delivered
• Secure long-term management funding

This mechanism is commonly used to secure both on-site and off-site biodiversity enhancements.

What is a habitat management and monitoring plan?

A habitat management and monitoring plan is a key document that sets out how biodiversity enhancements will be delivered and maintained over the 30-year period.

It typically includes:

• Habitat creation specifications
• Monitoring schedules
• Reporting requirements
• Remedial measures if targets are not met

The HMMP forms part of the legal framework securing biodiversity gain and ensures long-term accountability.

How does BNG apply to nationally significant infrastructure projects?

Nationally significant infrastructure projects (NSIPs) are subject to the Development Consent Order regime rather than standard planning applications.

BNG has been extended to nationally significant infrastructure projects, although implementation is phased. NSIPs must also demonstrate biodiversity net gain, but procedural mechanisms differ from the Town and Country Planning regime.

Developers of NSIPs should seek specialist advice to ensure compliance with the relevant regulations.

What is the process for securing planning permission under BNG?

To secure planning permission where BNG applies, a developer must:

• Conduct a baseline habitat survey
• Calculate biodiversity units using the statutory biodiversity metric
• Design a scheme to achieve at least 10% uplift
• Prepare biodiversity gain plans
• Agree any necessary legal agreement or conservation covenant
• Submit documentation to the local planning authority

Planning permission is granted subject to a condition requiring approval of biodiversity gain plans before commencement.

What are the risks of non-compliance?

Failure to comply with BNG requirements can result in:

• Delays to planning permission
• Refusal of biodiversity gain plans
• Enforcement action
• Breach of legal agreement
• Financial and reputational damage

Because biodiversity must be maintained for at least 30 years, developers and land managers should carefully assess long-term obligations before entering into agreements. 

Why is early advice important?

BNG affects site design, viability, and land acquisition. Early ecological assessment allows developers to:

• Optimise on-site habitat design
• Reduce reliance on off-site units
• Align proposals with the Local Nature Recovery Strategy LNRS
• Ensure compliance with Schedule 7A of the Town and Country Planning Act 1990

Proper planning reduces risk and improves outcomes for both development and nature recovery.

Our team of ecologists and land managers have helped numerous clients over the years, including policy guidance for BNG in England.

We can assist with biodiversity net gain by providing:

• BNG guidance
• Assessments
• Mitigation

If you would like to find out more about the services we provide, feel free to contact us using the details below.