Biodiversity Gain Plan

The introduction of mandatory Biodiversity Net Gain (BNG) under the Environment Act 2021 represents one of the most significant shifts in UK planning law in decades. A biodiversity gain plan is now a statutory requirement for most planning permissions, ensuring that new developments contribute to the recovery of nature by delivering a minimum 10% increase in biodiversity value. This legal mandate ensures that the natural environment is left in a measurably better state than it was prior to development.

For developers, homeowners, and planning professionals, the biodiversity gain plan is the critical document that demonstrates how this 10% uplift will be achieved, managed, and maintained for at least 30 years. At Approved Planning, we provide the technical precision required to navigate these ecological requirements, bridging the gap between your site feasibility goals and the rigid expectations of local planning authorities.

• Mandatory Requirement: A 10% uplift in biodiversity value is legally required for most planning applications in England.
• The Statutory Metric: Calculations must use the official Department for Environment, Food & Rural Affairs (DEFRA) statutory biodiversity metric.
• Mitigation Hierarchy: Developers must first avoid impact, then minimise, and only as a last resort compensate for biodiversity loss.
• 30-Year Commitment: Enhancements must be legally secured and managed for a minimum period of 30 years.
• Submission Timing: While biodiversity information is needed at the application stage, the formal biodiversity gain plan is typically submitted after permission is granted but before development commences.
• Off-site Solutions: If the 10% target cannot be met on-site, developers must purchase biodiversity units from off-site providers or statutory credits.

Understanding the Statutory Framework

The requirement for a biodiversity gain plan is rooted in the Environment Act 2021, which amended the Town and Country Planning Act 1990. The primary objective is to move away from simply protecting existing habitats toward a proactive model of environmental restoration. This framework applies to both “major” developments and “small sites,” although the latter may benefit from a simplified metric version.

It is essential to understand that biodiversity net gain is not a voluntary “green” initiative; it is a material consideration in the determination of planning applications. Failure to provide a robust strategy for achieving the 10% uplift can lead to significant delays, refusal of permission, or the inability to discharge pre-commencement conditions.

The Role of the Biodiversity Gain Plan

The biodiversity gain plan serves as the definitive roadmap for a project’s ecological impact and enhancement. It is a formal document submitted to the Local Planning Authority (LPA) that details how the development will meet the biodiversity gain objective. We ensure that these plans are meticulously prepared to withstand the scrutiny of council ecologists and planning officers.

The plan must include detailed information regarding:

• The pre-development biodiversity value of the onsite habitat.
• The steps taken to adhere to the mitigation hierarchy.
• The post-development biodiversity value of the onsite habitat.
• Any registered off-site biodiversity gains allocated to the development.
• Any statutory biodiversity credits purchased from the government.

Biodiversity Net Gain Requirements by Development Type

Development Category	Implementation Date	Core Requirement
Major Developments	February 2024	Full Statutory Metric / 10% Uplift
Small Sites	April 2024	Small Sites Metric / 10% Uplift
Nationally Significant Infrastructure (NSIP)	Expected 2025	Project-specific ecological mandates
Exemptions (e.g., Householder)	N/A	Standard ecological protection only

The Mitigation Hierarchy: A Strategic Approach

A central pillar of the biodiversity gain plan is the application of the mitigation hierarchy. This is a sequential approach that developers must follow to ensure that the ecological impact of a project is handled responsibly. Local authorities expect to see clear evidence that this hierarchy has been integrated into the site design from the earliest stages of site feasibility.

The hierarchy consists of four distinct stages:

1. Avoidance: Designing the project to avoid harm to high-value habitats (e.g., ancient woodland or veteran trees).
2. Minimisation: Where impact is unavoidable, reducing the scale of the damage through careful site layout and construction management.
3. On-site Restoration/Enhancement: Improving existing habitats or creating new ones within the red-line boundary of the application.
4. Offsetting: As a final resort, providing off-site gains to compensate for residual losses that cannot be managed on-site.

We advise our clients that relying heavily on the final stage—offsetting—can be cost-prohibitive. A well-conceived site feasibility assessment will identify ecological constraints early, allowing for a design that maximises on-site biodiversity value and reduces the need for expensive off-site credits.

Calculating Biodiversity Value: The Statutory Metric

The “value” of biodiversity is no longer a subjective assessment. It is determined using the Statutory Biodiversity Metric, a calculation tool provided by DEFRA. This tool uses “biodiversity units” to represent the relative value of different habitats based on their type, size, condition, and strategic significance.

The metric assesses three main types of biodiversity units:

• Area units: Applied to habitats such as grasslands, woodlands, and wetlands.
• Hedgerow units: Applied to linear boundary features.
• Watercourse units: Applied to rivers, streams, and canals.

It is important to note that these units are not interchangeable. If a development results in the loss of hedgerow units, the 10% gain must be achieved in hedgerow units specifically. You cannot trade a loss in watercourses for a gain in grassland. This “trading rule” ensures that specific types of nature are not phased out in favour of easier-to-implement habitat types.

Pre-Development vs. Post-Development

The first step in any biodiversity gain plan is establishing the baseline. A qualified ecologist must survey the site to determine the current biodiversity value. If a site has been cleared of vegetation prior to a survey in an attempt to lower the baseline, the legislation allows the LPA to use historical data (e.g., satellite imagery) to set a higher baseline value, effectively penalising habitat destruction.

The post-development value is then estimated based on the proposed landscaping and habitat management plans. The difference between these two figures must show a minimum 10% surplus to satisfy the statutory requirements.

On-site vs. Off-site Biodiversity Gains

While the preference of most planning authorities is for biodiversity to be enhanced on-site, this is not always physically or economically viable. Dense urban developments or small-scale residential infills may lack the space required to generate a 10% uplift. In these cases, the biodiversity gain plan must detail how the shortfall will be addressed.

On-site Enhancements

On-site gains are typically achieved through high-quality landscaping, the creation of wildflower meadows, sustainable drainage systems (SuDS) with ecological value, and the planting of native tree species. These features must be secured for 30 years, often through a Section 106 agreement or a conservation covenant. We work closely with landscape architects to ensure these designs are both aesthetically pleasing and ecologically compliant.

Off-site Biodiversity Units

If the 10% target cannot be met within the site boundary, developers can purchase biodiversity units from third-party landowners. These landowners “bank” biodiversity gains by improving their own land and then selling the resulting units to developers. These off-site gains must be registered on the national biodiversity gain site register to be legally recognised.

Statutory Biodiversity Credits

As a last resort, the UK government sells statutory biodiversity credits. These are intentionally priced high to discourage their use and to ensure the private market for biodiversity units remains the primary mechanism for delivery. Using statutory credits requires a clear justification in your biodiversity gain plan, proving that no on-site or off-site options were available.

The 30-Year Management and Monitoring Requirement

A biodiversity gain plan is not merely a “snapshot” of a site at the point of completion. It is a long-term commitment to the environment. Any habitat created or enhanced to meet the 10% requirement must be maintained in the specified condition for a minimum of 30 years.

This requirement introduces a new layer of complexity for developers and management companies. The plan must include a Habitat Management and Monitoring Plan (HMMP), which outlines:

• Who is responsible for the ongoing maintenance of the habitats.
• What specific management actions will be taken (e.g., grazing, mowing regimes, invasive species control).
• The schedule for monitoring reports to be submitted to the LPA.
• How the success of the habitat creation will be measured against the metric’s condition targets.

For many developers, this 30-year liability is a significant factor in the long-term financial planning of a project. Whether you are seeking full planning permission for a residential scheme or a commercial development, we can advise on the most sustainable ways to structure these long-term obligations.

Navigating Small Sites and Exemptions

While the 10% mandate is broad, there are specific exemptions and simplified procedures for smaller projects. Understanding these nuances is vital for homeowners and small-scale developers who wish to avoid the overheads associated with full-scale ecological assessments.

What is a “Small Site”?

In the context of biodiversity net gain, a small site is generally defined as:

• Residential development where there are between 1 and 9 dwellings on a site of less than 0.5 hectares.
• Residential development where the number of dwellings is unknown but the site area is less than 0.5 hectares.
• Non-residential development where the floor space created is less than 1,000 square metres or the site area is less than 1 hectare.

Small sites can use the “Small Sites Metric” (SSM), which is a simplified version of the statutory metric. It requires less data but still demands a 10% uplift. However, the SSM cannot be used if high-value habitats or protected species are present on the site.

Exemptions from Biodiversity Net Gain

Certain types of development are currently exempt from the requirement to provide a biodiversity gain plan. These include:

• Householder applications: Improvements to existing homes, such as extensions or loft conversions, provided they do not create a new dwelling.
• Small-scale self-build and custom-build: Developments of no more than 9 dwellings on a site of no more than 0.5 hectares that meet the legal definition of self-build.
• De minimis impacts: Developments that do not impact a priority habitat and affect less than 25 square metres of habitat or 5 metres of linear habitat (like a hedge).
• Permitted development rights: Most developments under permitted development rights do not currently require a biodiversity gain plan, though this is subject to specific criteria.

Common Pitfalls in Biodiversity Planning

In our experience, the complexities of BNG often lead to avoidable errors that jeopardize the success of a planning application. Precision is paramount when dealing with ecological data.

1. Inaccurate Baseline Assessment

Underestimating the value of the existing habitat can lead to a plan being rejected. If the LPA suspects the baseline has been artificially lowered, they have the power to intervene. Using a qualified ecologist to conduct a thorough baseline survey is non-negotiable.

2. Failure to Apply the Trading Rules

The metric is not just about the total number of units; it is about the *type* of units. Replacing a complex scrubland with a simple lawn will not satisfy the trading rules, even if the total unit count increases. The biodiversity gain plan must reflect a “like-for-like” or “like-for-better” approach.

3. Ignoring the Strategic Significance Multiplier

The metric rewards habitats that are created in areas identified as strategically important for nature (e.g., in a Local Nature Recovery Strategy). Failing to account for this can result in a lower unit score than expected, necessitating more land or more credits to reach the 10% target.

4. Lack of Long-Term Funding

LPAs will scrutinize the viability of the 30-year management plan. If there is no clear evidence of how the maintenance will be funded (e.g., through service charges or a sinking fund), the plan may be deemed undeliverable.

Integrating BNG into the Planning Process

Successful delivery of a biodiversity gain plan requires early integration. It should not be treated as an “add-on” after the site layout has been finalised. Instead, it should inform the very first sketches of the project.

Our strategic approach involves three main phases:

Phase 1: Pre-Application Feasibility

We conduct an initial assessment of the site’s ecological potential. By identifying high-value areas early, we can design around them, significantly reducing the cost of mitigation. This stage also involves checking local policy to see if the council requires more than the 10% national minimum—some local authorities in London and the Southeast are already targeting 20%.

Phase 2: The Planning Application

At the submission stage, we provide a “Biodiversity Net Gain Statement.” This is not the final plan, but it demonstrates to the LPA that the 10% uplift is achievable within the proposed design. This gives the council the confidence to grant permission, usually with a condition that the final biodiversity gain plan be submitted and approved before work begins.

Phase 3: Post-Permission Compliance

Once permission is granted, we refine the biodiversity data into a formal plan. We coordinate with ecologists, landscape architects, and legal professionals to secure the 30-year management agreements and, if necessary, facilitate the purchase of off-site units or statutory credits.

The Future of Biodiversity in UK Development

The shift toward mandatory biodiversity net gain is part of a broader trend toward “Environmental Net Gain.” In the future, we expect to see similar mandates for water neutrality and carbon sequestration within the planning system. By mastering the biodiversity gain plan process now, developers can future-proof their portfolios against increasingly stringent environmental regulations.

At Approved Planning, we remain at the forefront of these policy changes. We ensure that our clients are not merely reacting to new laws but are using them strategically to enhance the value and viability of their developments. The goal is a seamless transition from architectural vision to successful local authority approval, with nature recovery integrated as a core asset rather than a regulatory hurdle.

Frequently Asked Questions

Does every planning application require a biodiversity gain plan?

No. While the mandate is broad, exemptions exist for householder applications (like home extensions), small-scale self-build projects, and developments with a “de minimis” impact on habitats. However, most new residential and commercial developments now require one.

Can I achieve the 10% uplift just by planting trees?

Not necessarily. The biodiversity gain plan must follow the statutory metric’s “trading rules.” This means you must replace the specific type of habitat lost. If you remove a meadow, you generally need to create or enhance a meadow, not just plant trees, to satisfy the metric’s requirements.

What happens if I cannot reach the 10% target on my site?

If on-site enhancements are insufficient, you must look off-site. You can buy biodiversity units from a landowner who has registered their land for BNG, or as a final resort, purchase statutory credits from the government. These costs must be factored into your development budget.

Who monitors the site for the required 30-year period?

Responsibility lies with the landowner or the developer, often delegated to a management company. The biodiversity gain plan will include a monitoring schedule, and reports must be submitted to the Local Planning Authority to prove the habitats are reaching their target condition.

How much does a biodiversity gain plan cost to produce?

The cost varies significantly based on the size of the site and the complexity of the habitats involved. Costs include the ecologist’s survey fees, the calculation of the metric, the drafting of the management plan, and potential legal fees for Section 106 agreements. We provide transparent fee structures to help you manage these costs effectively.

Is BNG required for Prior Approval or Lawful Development Certificates?

Generally, BNG requirements do not apply to Lawful Development Certificates because they confirm existing lawfulness rather than granting new permission. However, for certain Prior Approval applications, particularly those involving a change of use that requires physical development, you should check the current guidance as the rules are subject to specific legislative triggers.

What is the “statutory biodiversity gain condition”?

Every planning permission granted in England (unless exempt) is now subject to a “deemed” condition. This condition states that development cannot begin until a biodiversity gain plan has been submitted to and approved by the planning authority. This makes the plan a critical milestone in the development timeline.