Exploring how mandatory Biodiversity Net Gain (BNG) works

Mandatory Biodiversity Net Gain (BNG) for most major developments in England comes into force on 12 February, with requirements for small sites following on 2 April.

In this article we explore what the new legislation means for developers and how the BNG process will work in practice.

What is BNG?

BNG is an approach to development and land management that aims to leave biodiversity in a measurably better state than it was beforehand. The policy is a key part of the government’s commitment to reversing biodiversity decline by 2030.

For the purposes of BNG, biodiversity is calculated using the statutory biodiversity metric, a calculation tool that quantifies the biodiversity value of a site before and after development. This value depends on factors such as the type, size, and quality of habitats present, and on-site location. Units can be lost through development or generated through habitat enhancement or creation.

In addition to achieving 10% net gain, BNG must be delivered under the mitigation hierarchy (avoid, minimise, restore, compensate), good practice requirements, and satisfy the trading rules i.e. where the mitigation measures have to be appropriate for the habitat types impacted.

Veteran Oak tree
Veteran Oak tree
Who will it affect?

Most major developments that fall under the Town & Country Planning Act in England will be required to deliver at least 10% BNG from 12 February. This includes residential developments of 10 or more dwellings or where the total site area is greater than 0.5 hectares. It also includes other developments where the change in proposed floor space is over 1,000 square metres, or total site area is over 1 hectare.

Requirements for small sites come into force from 2 April.

Some developments will be exempt from BNG. These include householder applications, developments below the threshold, and some self-build applications. However, many local authorities have their own BNG policies and targets, with some requiring gains in excess of 10%.

How will it work in practice?

From 12 February 2024, planning applications will need to be accompanied by a statement confirming whether a development is exempt from BNG. If BNG is required, a biodiversity metric calculation tool showing the site’s pre-development baseline biodiversity value will need to be provided, alongside information on how biodiversity gains will be provided. These must be completed by a competent person, normally an ecologist.

Local policies may have additional requirements for the information provided at application submission.

Once planning permission is granted, a Biodiversity Gain Plan must be submitted and approved by the Local Planning Authority (LPA) before works commence. This plan sets out how BNG requirements will be met. It must include a completed metric calculation and pre- and post-development plans. Once submitted the LPA has eight weeks to approve or refuse the plan.  Land delivering off-site gains and significant on-site enhancements will need to be legally secured, managed, maintained, and reported on for a minimum of 30 years. This will be achieved through a legal agreement and a Habitat Management and Monitoring Plan (HMMP).

A design-led approach for the delivery of biodiversity gains is recommended to maximise the potential of the development and enable consideration of factors such as how habitat enhancements will interact with other land uses. The ability of the project to deliver net gain on site will impact the legal agreements such as planning conditions or S106 agreements which will need to be secured in granting planning permission.

Applications for small sites may be able to use a simpler version of the metric tool known as the small sites metric (SSM), although exceptions apply.

How does BNG fit in with existing legislation?

BNG is additional to existing habitat and species protections. It is intended to complement biodiversity initiatives such as nutrient neutrality, green infrastructure, and local nature recovery strategies.

It is intended to reinforce and complement the mitigation hierarchy, whereby negative impacts should first be avoided, then minimised, adequately mitigated, or as a last resort, compensated for.

How will it change the development process?

The delivery of biodiversity gains will be legally required and should be considered as early as possible in the design process.

Engaging early with BNG and the mitigation hierarchy will minimise the potential impacts of a project and maximise potential onsite gains, reducing the need for off-site solutions or costly credits. It also means potential constraints can be identified at a time when more flexible design solutions can be considered.

We have over a decade of experience in biodiversity offsetting and environmental design so we can guide you through the BNG process. From site selection and baseline surveys, to landscape design and management plans, our in-house team of Ecologists and Landscape Architects will work with you to maximise your site’s biodiversity potential.

For further information visit gov.uk.

Dave has over ten years’ experience as a consultant ecologist and is our Lead Ecologist. He has worked on a wide variety of projects, to which he brings together his problem-solving background in engineering, ability to use AutoCAD and knowledge gained from his masters in Ecological Impact Assessment (EcIA).

Recent Articles

See more