Biodiversity Net Gain 2024: Guidance on new rules

In 2024, Biodiversity Net Gain (BNG) emerges as a leading force in the United Kingdom’s efforts toward environmental conservation and sustainable development. BNG represents an innovative approach requiring developers to leave the natural environment in a measurably better state than before their projects commenced.

As a result of the Environment Act 2021, Biodiversity Net Gain is set to become a mandatory practice for all development proposals in the UK. Developers must adhere to BNG principles and ensure their projects meet its criteria. Additionally, developers will have to guarantee that BNG is secured for at least 30 years.

In January 2024, the UK government released additional guidance on BNG ahead of its implementation. Furthermore, BNG’s official implementation date is confirmed for February 12, 2024.

What types of development will BNG apply to?

From 12 February 2024, BNG will be mandatory for new planning applications for major development made under the Town and Country Planning Act 1990. Major developments include residential developments with 10 or more dwellings or if the site area is greater than 0.5 hectares.

Biodiversity net gain will be made mandatory for small sites from April 2024. Small sites include residential developments where the number of dwellings is between 1 or 9 or if the site area is less than 0.5 hectares. Small sites also include commercial developments where floor space created is less than 1000 square metres or the overall site area is less than 1 hectare.

Updates to BNG related legislation

In November, a draft of the secondary legislation package was released to assist stakeholders in readiness for mandatory BNG. Following this, some slight modifications were made to the legislation’s wording. Notably, there has been considerable focus on the de-minimis exemption and the biodiversity gain hierarchy. Based on conversations with stakeholders, clarifications and modifications have been introduced.

Why is BNG being required by local planning authorities?

BNG is significant for a variety of reasons and can help to positively affect the surrounding environment and wildlife. Some of the main benefits that BNG provides include:

• It supplies oxygen and water to the surrounding environment
• Enhances the visual appearance of the environment
• Facilitates a scientific understanding of the environment
• Provides jobs for agricultural occupations
• Helps to protect special scientific interest sites, nationally significant infrastructure projects, and irreplaceable existing habitats

The concept of mandatory biodiversity net gain planning condition is a structured method of ensuring that all of the factors listed above are encouraged and supported in the years ahead.

As BNG applies to all planning projects, it causes a universal approach from governing bodies and local authorities. Therefore, due to the fact that BNG is a government policy, it prevents any potential issues with key stakeholders.

Implementing BNG

If you are uncertain about the potential impact of mandatory biodiversity net gain on your planning application, it is advisable to reach out to your local planning authorities as soon as possible. They can provide detailed insights into your development plans and assess their alignment with BNG requirements and planning obligations.

Should your authorities suggest that your development might face significant implications, we advise seeking assistance from a knowledgeable ecologist. Our ecologists can evaluate whether your plans meet the necessary standards and suggest any measures you may need to implement to adhere to biodiversity requirements.

Our team has strong experience completing BNG and will provide guidance throughout the planning process. We can ensure that one of our experienced biodiversity ecologists visits your development site to create and develop any required BNG reports using biodiversity metrics. Our team can also assist with habitat enhancements by using a Natural England habitat management and monitoring plan template.

Biodiversity net gain plans

In order to obtain planning permission for a project from a local planning authority, developers must be able to prove that they are taking the correct measures to increase BNG. One of the first steps in this process is to book an experienced ecologist to create a biodiversity gain plan.

Depending on the ecologist’s findings within a biodiversity net gain assessment, the BNG plan will help to determine natural elements that could potentially be at risk as a result of the development project. The plan will also detail any mitigation methods, such as conservation covenants or habitat recreation, to be taken in order to prevent these outcomes from occurring both on site and off site.

The aim is to get clients to think about biodiversity during the initial planning and design stages and avoid retrofitting once designs have been produced. Retrofitting will often lead to delays, unpredicted financial costs and difficulties with planning application determinations.

How can we assist?

Our team of ecologists and land managers have helped numerous clients over the years, including policy guidance for delivering Biodiversity Net Gain 2024.

We can assist with biodiversity net gain by providing:

• BNG guidance
• Assessments
• Mitigation
• BNG plans
• Land management

Please get in touch if you would like further information about further biodiversity net gain 2024 guidance. We are happy to offer free CPD sessions on the BNG principles and how we can help your schemes achieve this.

Our Ecology Director, Olivia Collington, holds a Natural England license. If you would like to find out more about the services we provide, feel free to contact us using the details below.

Current position: mandatory BNG is already in force

Mandatory biodiversity net gain is no longer a future change. In England, it began on 12 February 2024 for major development and 2 April 2024 for small sites, subject to exemptions and transitional arrangements. These commencement dates generally relate to when the planning application was made, rather than simply when permission was granted.

The Environment Act 2021 introduced the statutory framework requiring relevant development to achieve at least 10% biodiversity net gain. This is a measurable increase in habitat value, not a requirement to leave 10% of a site undeveloped or plant 10% more trees. The statutory biodiversity metric provides the calculation, while planning controls and legal agreements secure delivery.

For development subject to the biodiversity gain condition, the local planning authority must approve a biodiversity gain plan before development starts. Planning permission alone does not discharge that condition. The government's planning practice guidance explains the statutory framework and its relationship with planning decisions.

Establish whether the rules apply to your proposal

Application dates, development type and the scope of any exemption should be checked before commissioning a detailed delivery strategy. Householder development and qualifying self-build or custom-build proposals are among the categories with exemptions, but each has its own requirements. The de minimis exemption also has specific habitat-impact thresholds; a small development is not automatically exempt.

Transitional arrangements can affect applications linked to earlier permissions. Outline permissions, reserved matters and applications to vary conditions need careful review rather than assumptions based on the latest submission date. Our guide to BNG exemptions can help identify the questions to resolve.

BNG does not replace protected species legislation, designated-site safeguards or the mitigation hierarchy. A scheme may need ecological surveys and mitigation even where mandatory BNG does not apply. Equally, achieving a numerical uplift does not make otherwise unacceptable habitat loss acceptable.

Build the calculation around a reliable habitat baseline

A habitat baseline survey establishes what is present before development. An ecologist typically uses UKHab to classify terrestrial habitats, supported by mapped boundaries, photographs and a condition assessment where the metric requires one. Hedgerows and watercourses need appropriate assessment and are accounted for separately from area habitats.

Survey timing matters. Some habitats can be identified throughout much of the year, while others need seasonal botanical evidence. An early walkover may flag constraints without providing everything required for a defensible final calculation. Existing records, aerial photography and previous land management can also inform the baseline.

The statutory biodiversity metric considers habitat extent, distinctiveness, condition and strategic significance. Proposed habitats are additionally affected by delivery risks, including the time needed to reach target condition and the difficulty of establishing them. For qualifying small developments, the Small Sites Metric may be available, subject to its eligibility rules.

Deliberately degrading habitat does not provide a legitimate route to reducing BNG requirements. Anti-degradation provisions can require an earlier habitat value to be used. A BNG consultant should investigate relevant site history before treating the current condition as the accepted starting point.

Follow the biodiversity gain hierarchy

Design should first consider how to avoid habitat impacts and retain valuable ecological features. The statutory biodiversity gain hierarchy then guides decisions about enhancement, creation and off-site provision. It is not simply a choice between landscaping a site and purchasing units.

Where appropriate on-site delivery cannot meet the requirement, registered off-site biodiversity units can address the remaining shortfall. These may come from the developer's own land or a third-party habitat bank. The habitat types and unit categories must satisfy the metric's trading rules; an area-habitat surplus cannot simply cancel a hedgerow or watercourse deficit.

Location also matters. Spatial risk factors can reduce the contribution of off-site units when they are supplied farther from the development. Separately, strategic significance reflects how habitat proposals align with identified ecological priorities. Relevant Local Nature Recovery Strategies, or LNRS, should inform assessment in accordance with current metric guidance and locally applicable evidence.

Statutory biodiversity credits are a last resort, purchased from government where on-site and off-site options cannot meet the requirement. They are not the same product as privately supplied biodiversity units.

Prepare the biodiversity gain plan before starting work

A biodiversity gain plan explains how the development will achieve its required uplift. It brings together the baseline, completed metric, proposed habitat outcomes and any allocated off-site gains or statutory credits. For phased development, special arrangements apply, including an overall plan and subsequent phase plans.

The plan should be consistent with approved drawings and the practical management arrangements. For example, a meadow shown in the metric must not become an intensively mown amenity area in the landscape specification. Drainage, access, utilities and maintenance requirements should be checked before habitat commitments are finalised.

Early coordination between the ecologist, planner, landscape designer and legal advisers reduces the risk of conflicting documents. Our biodiversity gain plan guidance explains how this evidence fits together.

Secure habitats and budget for their management

Significant on-site enhancements and off-site gains must be maintained for at least 30 years. Off-site gains require a conservation covenant or section 106 agreement and registration on the biodiversity gain site register operated by Natural England. Relevant gains must also be allocated to the development that will use them.

A habitat management and monitoring plan translates the calculation into practical work. It should identify establishment methods, management prescriptions, monitoring intervals, reporting responsibilities and corrective action if habitat condition falls behind target. The legal documents should make responsibility for funding and delivery clear.

Before committing to a design or unit purchase, check the complete delivery route: survey evidence, metric compliance, legal security, registration, allocation and long-term management. An experienced BNG consultant can coordinate these elements, helping the project move from a numerical target to an achievable, enforceable habitat outcome.