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Biodiversity Net Gain: What Developers in England Need to Know

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Lucy Dixon, sustainability lead for Veriforce CHAS, considers the impact of new Biodiversity Net Gain (BNG) requirements for developers of smaller sites in England.

The Biodiversity Net Gain (BNG) framework, mandated under the Environment Act 2021, officially launched on 12th February 2024 and requires a minimum 10 per cent BNG for planning permission with an extended transition period for small sites until 2nd April 2024. This means developers must submit plans to their Local Planning Authority (LPA) showing how their project will contribute to an overall increase in the quality or quantity of the natural habitat of the site on which they are situated – with some LPAs demanding increases of more than 10%.

For major developers, incorporating BNG into project designs will likely not be entirely new. For smaller projects, however, the implications of the policy might be more keenly felt. Constraints in resources, finances and the space available to implement biodiversity offsetting measures can all pose a challenge to the viability of small site developments.

Purpose of BNG

The fourth State of Nature (SON) Report, unveiled in September 2023, highlighted the alarming decline of biodiversity in the UK. The report underscored the UK’S ongoing environmental degradation, which is already acknowledged as one of the most nature-depleted nations globally.


The data revealed a troubling trend, indicating that since 1970, UK species have, on average, experienced a 19% decline, with almost 1 in 6 species (16.1%) now facing the imminent threat of extinction. It’s clear that urgent action is required, and the BNG framework supports this. 

Small sites definition and the small sites metric

In the context of the Biodiversity Net Gain (BNG) framework, small sites are defined as:

•   Residential Developments: Dwellings numbering between 1-9 on a site measuring less than one hectare, or in cases where the number of dwellings is unknown, on a site area less than 0.5 hectares.

•   Non-Residential Sites: Encompassing areas where the floor space created is less than 1,000 square meters or where the site area is less than one hectare.

Certain exemptions exist within the BNG policy, notably for small self-build and custom homebuilding sites.

Appointing a competent person 

Developers overseeing small sites must designate a competent person (referred to as the SSM ‘user’) to carry out a Small Sites Metric (SSM) assessment using the SSM tool. A competent person does not have to be an ecologist but they must have the necessary knowledge and experience in line with the British Standard Process for designing and implementing biodiversity net gain: BS 8683:2021 to perform and review SSM calculations.

SSM users should demonstrate competence in the following areas:

•       Identifying pre-development habitats on the site

•       Understanding management requirements for habitats to be created or enhanced in the post-development landscape design

The Small Sites Metric can be used on projects that qualify as a minor development and on land where there are no priority habitats present. The list of priority habitats requiring conservation include, for example, ancient hedgerows, traditional orchards and lowland meadows. Larger developments should refer to The Statutory Biodiversity Metric.

How can developers achieve BNG?

Government guidance sets out three ways a developer can achieve 10% BNG:

•   They can enhance and restore biodiversity on-site (within the red-line boundary of a development site). 

•   If developers can only achieve part of their BNG on-site, they can deliver through a mixture of on-site and off-site. Developers can either make off-site biodiversity gains on their land outside the development site or buy off-site biodiversity units on the market.

•   If developers cannot achieve on-site or off-site BNG, they must buy statutory biodiversity credits from the government, with the government using the revenue to invest in habitat creation in England. This must be a last resort.

Developers can combine all three options but must follow the steps in order. This order of steps is called the biodiversity gain hierarchy. 

For small site developers, particularly those with limited land availability, familiarising themselves with the details of the biodiversity gain hierarchy is key to the success of their projects achieving planning permission. 

Incentives for developers

BNG policy offers opportunities for innovation, especially for smaller developers. For example, incorporating green infrastructure or biodiversity-friendly design elements (such as a wildflower roof) can enhance a project’s marketability and value.

Fulfilling BNG requirements can foster collaboration, easing compliance burdens. Engaging stakeholders like landowners, ecologists, and environmental organisations early in the planning process can address potential issues. Pooling resources and expertise not only maximise biodiversity enhancement for the current project but also establish a cost-effective blueprint for future developments.


While mandatory BNG poses challenges for small development sites, it also presents opportunities for collaboration, innovation, and creative problem-solving. Recognising the intrinsic value of nature is essential for contributing positively to biodiversity conservation and ensuring its significance for current and future generations.

Lucy Dixon

Lucy Dixon is the product manager for UK compliance solutions provider, CHAS' Fairness, Inclusion & Respect (FiR) assessment.


  • Lucy Dixon

    Lucy Dixon is the product manager for UK compliance solutions provider, CHAS' Fairness, Inclusion & Respect (FiR) assessment.

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