Biodiversity Net Gain (BNG) is a framework designed to ensure that developments leave the natural environment in a better state than before. With the UK’s biodiversity under increasing pressure, BNG offers a way to balance economic growth with ecological restoration. It ensures that development projects result in an overall improvement in biodiversity, contributing to the UK’s broader environmental goals.
What is Biodiversity Net Gain?
In the UK, BNG requires developers to leave the natural environment in a better condition than it was before their projects began. Mandated by the Environment Act 2021, most new developments in England must deliver at least a 10% net gain in biodiversity, calculated using the Defra Biodiversity Metric. This metric assesses the ecological value of existing habitats based on their type, quality, distinctiveness and condition.
For example, if a development leads to the loss of 1 hectare of low-quality grassland, the developer might compensate by creating 1.2 hectares of higher-quality wildflower meadows nearby or by enhancing an existing habitat. The goal is to ensure that any ecological losses from a development are outweighed by biodiversity gains so that the development ultimately delivers tangible wildlife and ecosystem benefits.
Why is BNG Important in the UK?
Many people argue that the UK is currently facing a biodiversity crisis, with significant habitat loss and species declines over recent decades. Reports such as the State of Nature 2019 highlight that 41% of UK species have declined since 1970. Drivers of this decline include urbanisation, agricultural intensification and climate change.
BNG represents a proactive response to this crisis by embedding nature recovery into property development. It aligns with the government’s 25-Year Environment Plan, which aims to reverse biodiversity loss, improve natural capital and leave the environment in better shape for future generations.
Why is BNG important for development and environmental conservation?
BNG is important as it provides a clear framework that allows new developments to move forward without sacrificing the natural environment. For developers, it offers a structured way to meet environmental responsibilities while still delivering projects. For conservation, it’s a tool to reverse habitat loss, support species recovery, and strengthen ecosystem resilience.
An Overview of the UK’s commitment to biodiversity and sustainability.
The UK’s Commitment to Biodiversity and Sustainability is reflected in both policy and law. Under the Environment Act 2021, BNG is now mandatory in England, with most new developments required to deliver at least a 10% net gain in biodiversity. This aligns with the UK’s international commitments, including the Convention on Biological Diversity and the Kunming-Montreal Global Biodiversity Framework, which aim to halt and reverse nature loss by 2030.
How does BNG contribute to the 25 Year Environment Plan?
BNG also plays a major role in delivering the government’s 25 Year Environment Plan, particularly the goal of embedding an environmental net gain principle in development, including housing and infrastructure. By making nature a core part of planning and construction, BNG ensures that growth and environmental recovery go hand in hand.
Biodiversity Net Gain (BNG) is now mandatory in England under the Environment Act 2021. From February 2024, all major development projects are legally required to deliver at least a 10% net gain in biodiversity. This requirement will extend to small sites starting in April 2024, as part of a phased rollout.
How Does Biodiversity Net Gain Work in Practice?
Baseline Habitat Assessment: Developers must first arrange a Biodiversity Net Gain survey to establish its current biodiversity value, using the Defra Biodiversity Metric.
Design for Avoidance and Minimisation: The project is designed to avoid harming high-value habitats (e.g. irreplaceable habitat, such as ancient woodlands) and minimise impacts on other features.
Compensation Through Habitat Creation: Where harm cannot be avoided, developers must deliver compensatory measures. These could include creating new habitats, such as grasslands, woodlands or wetlands, or improving the condition of nearby habitats.
Long-Term Monitoring and Management: Biodiversity gains must be secured and effectively managed for at least 30 years. Compliance being overseen by the local planning authority, supported by appropriate conservation bodies.
BNG Calculation & Metrics
The statutory BNG metric is a tool developed by Defra (Department for Environment, Food & Rural Affairs) to consistently measure and account for changes in biodiversity value resulting from development. It uses habitat types, condition, distinctiveness, and strategic significance to calculate biodiversity units.
How to do a BNG calculation?
A BNG calculation involves assessing the pre-development biodiversity value of a site using the metric, predicting the post-development biodiversity value (including any on-site enhancements), and then calculating the required off-site or credit purchase to achieve at least a 10% net gain. This process requires ecological expertise and the use of the official BNG metric tool.
An overview of Defra’s Biodiversity Metric 4.0
As of April 2025, Defra’s Biodiversity Metric 4.0 is the current version of the statutory metric. It provides a standardized approach to measuring biodiversity, incorporating factors like habitat distinctiveness, condition, connectivity, and strategic significance. It also includes separate calculations for linear features like hedgerows and watercourses.
Understanding Biodiversity Units
Biodiversity units are the currency used in the BNG metric. There are currently three different types of units to account for various habitat features:
Area-based units: Used for habitats like grasslands, woodlands, and wetlands, calculated based on area and condition.
Hedgerow units: Calculated based on the length and condition of hedgerows.
Watercourse units: Calculated based on the length and condition of rivers, streams, and other watercourses.
The baseline assessment is the first step in the BNG process. It involves a detailed ecological survey of the development site to determine the existing habitat types, their condition, and their overall biodiversity value. This provides the starting point against which any loss or gain will be measured using the statutory metric.
What is Rule 5 of BNG?
Rule 5 of the BNG regulations, as outlined in The Biodiversity Gain Requirements (Exemptions) Regulations 2023, states that the biodiversity gain condition does not apply to planning applications for householder developments. If a development is considered a householder application, it is exempt from the mandatory BNG requirement.
How do LPAs assess BNG plans?
LPAs will assess Biodiversity Gain Plans submitted with planning applications to ensure they:
Accurately reflect the pre-development biodiversity value.
Demonstrate how the 10% net gain will be achieved through on-site and/or off-site measures.
Include details of habitat creation, enhancement, and long-term management.
Comply with the statutory metric and relevant guidance.
Legal Framework & Regulatory Requirements
The BNG framework in the UK requires that most developments deliver a 10% net gain in biodiversity, measured against a pre-development baseline, which must be maintained for 30 years.
What are the biodiversity net gain requirements in the UK?
Developers must measure biodiversity on-site before any work begins and then show how they will leave nature in a better state, whether through on-site improvements, off-site habitat creation, or a government-run biodiversity credits scheme.
What is Section 14 of the Environment Act?
These requirements for BNG are set out in Section 14 of the Environment Act, which introduces Schedule 7A to the Town and Country Planning Act. This section legally embeds BNG into the planning system.
The Mandatory BNG start depends on the site. For major sites, BNG is mandatory from 12 February 2024. For small sites, BNG applies from 2 April 2024
Section 14 of the Environment Act amends the Town and Country Planning Act 1990 to make biodiversity gain a condition of planning permission in England (with some exemptions).
What is the role of LPAs in enforcing BNG?
The Local Planning Authorities are responsible for reviewing and approving Biodiversity Gain Plans, enforcing compliance, and monitoring long-term outcomes.
BNG Implementation Process & Compliance
A detailed biodiversity report, including a baseline assessment and BNG calculations using the statutory metric, is typically required to support a planning application subject to mandatory BNG.
A Biodiversity Gain Plan outlines how the required net gain will be achieved and maintained. It should include:
The baseline biodiversity value of the site.
Calculations demonstrating the 10% net gain.
Details of proposed on-site and/or off-site habitat creation and enhancement.
A clear management plan for at least 30 years.
Monitoring and reporting arrangements.
What is the mitigation hierarchy in the UK?
The mitigation hierarchy in the UK is a stepwise approach to minimising biodiversity loss from development.
It prioritises:
1. Avoidance: Preventing impacts on biodiversity in the first place.
2. Minimisation: Reducing the extent and intensity of unavoidable impacts.
3. Restoration: Repairing damage to habitats on-site.
4. Offsetting: Compensating for residual losses through off-site habitat creation or enhancement (this is where BNG comes in).
Habitat creation, enhancement and resoration strategies
Habitat creation, enhancement, and restoration strategies are central to achieving BNG and vary depending on the site. They typically involve designing and implementing measures to create new habitats, improve the condition of existing ones, or restore degraded areas to increase their biodiversity value. This can include planting native species or removing invasive species.
BNG requires the long-term management of the created or enhanced habitats for at least 30 years. This ensures the sustained delivery of biodiversity gains and often involves legal agreements. BNG requirements primarily apply to developments that involve physical works and habitat disturbance.
Is BNG required for a change of use?
A change of use of land or buildings may not automatically trigger BNG unless it involves such works. However, LPAs may assess the potential impact on biodiversity and require mitigation or enhancement in some cases.
What is a Section 106 agreement for biodiversity net gain?
A Section 106 agreement is a legally binding agreement between a developer and the LPA, often used to secure off-site biodiversity enhancements or long-term management obligations associated with BNG.
BNG Credits
BNG credits are used to help developers meet Biodiversity Net Gain (BNG) requirements when other mitigation options are exhausted. The number of BNG credits needed depends on the shortfall in biodiversity units after considering on-site mitigation and enhancement. This is calculated using the statutory metric.
How much do BNG credits cost?
The cost of statutory biodiversity credits varies depending on factors such as the type and location of the habitat being created or enhanced, the provider, and market demand. Statutory biodiversity credit costs vary greatly by habitat type and distinctiveness, requiring two credits per unit needed. As a last resort, discuss this option with your LPA for approval before applying, a process that can take up to 8 weeks.
Upon approval, you’ll receive an invoice to pay before submitting proof of purchase with your BNG plan. Developers should prioritize achieving the 10% net gain on-site. If this is not fully possible, off-site solutions involve creating or enhancing habitats on land away from the development site, often through agreements with landowners. Purchasing statutory biodiversity credits from the government is intended as a last resort when on-site and off-site options are not feasible. The revenue from these credits will be reinvested in habitat creation.
How much does a BNG survey cost?
The cost of a BNG survey depends on the size and complexity of the development site and the level of ecological expertise required. It can range from a few hundred to several thousand pounds. There is no fixed number of BNG units per acre. The number of units generated from a given area depends entirely on the type and condition of the habitat created or enhanced.
Exemptions from BNG
Certain types of development are exempt from mandatory BNG, including:
Small-scale developments (defined by specific criteria).
Householder applications.
Development below a de minimis threshold.
Brownfield land that meets specific criteria.
Nationally Significant Infrastructure Projects (NSIPs), which have their own biodiversity requirements.
The de minimis rule exempts developments where the impact on biodiversity is considered too small to warrant BNG requirements. This typically applies to very small-scale developments with minimal habitat loss. Specific thresholds are defined in regulations.
Do BNG regulations impact irreplaceable habitats?
Irreplaceable habitats, such as ancient woodland, are excluded from BNG offsetting. The focus is on avoiding any loss or degradation of these habitats in the first place.
What are the rules for previously degraded land?
While development on previously degraded land (brownfield sites) is generally encouraged, it is still subject to BNG requirements if it results in a loss of biodiversity value. However, the baseline biodiversity value may be lower, potentially reducing the scale of offsetting required.
Special considerations for large infrastructure projects (NSIPs)
Nationally Significant Infrastructure Projects (NSIPs) are subject to their own biodiversity assessment and mitigation requirements under separate consenting regimes. While the principles of net gain are often applied, the specific mechanisms differ from the standard BNG framework.
Long-term Monitoring, Compliance & Enforcement
LPAs are responsible for monitoring the implementation and long-term management of BNG sites. This may involve site visits, reviewing monitoring reports submitted by developers or landowners, and taking enforcement action if breaches of agreements occur.
What is a BNG Strategy?
A BNG strategy outlines how a developer or LPA will approach achieving net gain across a portfolio of projects or within a specific geographic area. It may include setting targets, identifying potential off-site locations, and establishing partnerships.
The role of the BNG site register
The Biodiversity Gain Site Register, managed by Natural England, records off-site biodiversity gain sites and the biodiversity units they generate. This helps to ensure transparency and track the delivery of off-site BNG.
LPA enforcement penalties for non-compliance
LPAs have powers to enforce BNG requirements through planning conditions and legal agreements. Non-compliance can lead to enforcement notices, potential fines, and delays in project completion.
Responsibilities of developers vs. landowners
Developers are responsible for ensuring that their projects achieve the required net gain. Landowners can play a crucial role by providing land for off-site BNG and entering into agreements for long-term management. The responsibilities are often defined in legal agreements.
Long-term habitat maintenance and conversation covenants
Long-term habitat maintenance is essential for the success of BNG. Conservation covenants are legal agreements that bind future landowners to the agreed-upon management plan for at least 30 years, ensuring the sustained delivery of biodiversity gains.
Challenges and Opportunities
While BNG has significant potential, it is not without its challenges. Crtics argue that the BNG metric can oversimplify complex ecosystems and place qual value on species and habitats that are more common and in less need of saving. Thus opportunities could be missed to fully appreciate the ecological value of some sites, which could result in their loss.
Another major concern is the reliance on off-site compensation. While BNG ideally encourages developers to enhance biodiversity within their project boundaries, in practice, many developments will offset their impact by funding habitat creation elsewhere. Ecologists fear that this could lead to the loss of valuable local ecosystems, particularly in urban areas, in exchange for biodiversity gains in remote locations that do not benefit the affected communities.
Initiatives such as the Nature Recovery Network aim to create a strategic approach to BNG, ensuring habitat enhancements contribute to wider ecological connectivity and national biodiversity goals.
Opportunities for Landowners & Investors
Landowners can generate income by creating and managing habitats on their land and selling the resulting biodiversity units to developers who need to offset their biodiversity losses.
How to register land for BNG offsetting
Landowners can register their land as an off-site biodiversity gain site through the Biodiversity Gain Site Register, once a Biodiversity Gain Plan for the site has been approved.
Potential income from selling biodiversity units
The potential income for landowners depends on the number and type of biodiversity units generated, the local market demand, and the terms of agreements with developers or brokers.
Supply & demand for BNG units
The market for biodiversity units is expected to grow as mandatory BNG is implemented more widely. Understanding local supply and demand is crucial for landowners and developers.
What is the Biodiversity Strategy for 2030?
The UK’s biodiversity strategy for 2030 aims to halt the decline in species abundance by 2030 and sets out ambitious targets for nature recovery, aligning with international goals.
A Biodiverse Future
Despite the challenges surrounding BNG, there is general agreement that the principle of developments enhancing biodiversity is a good one.
It is still early days for BNG, and it is hoped that revisions and updates to the assessment and implementation processes will vastly improve its effectiveness.
In the meantime, there is much that consultants like Phlorum can do to help guide all sides through the BNG process, so that it delivers what is needed now. It is in everyone’s interest that truly sustainable development that benefits biodiversity continues to shape our shared future.
Dr Paul Beckett is one of the UK’s leading experts in Japanese knotweed and is a member of the Expert Witness Institute. He regularly provides Japanese knotweed expert witness services. He helped produce the RICS knotweed guidance for surveyors and was integral in the formation of the Property Care Association (PCA) Invasive Weed Control Group (IWCG).
