14th March 2024

Biodiversity Net Gain: why everyone is going ‘wild’ for BNG

By Hana Ghale

The introduction of Biodiversity Net Gain (BNG) is the biggest change to planning regulations in decades. It presents an approach to development with the sole purpose of ensuring wildlife habitats are left in a better state than before development and contributing positively towards nature’s recovery. In this article, we answer some frequently asked questions about BNG to help developers navigate this new mandatory planning permission condition.

Which developments does Biodiversity Net Gain (“BNG”) apply to?

The 2021 Environment Act explicitly made BNG a condition of planning permission, meaning it will apply to all planning permissions granted in England from April this year. All developers are required to demonstrate how they will deliver the statutory 10 per cent improvement to the biodiversity value of any application site. The mandatory requirement for BNG in developments is being rolled out throughout 2024 as follows:

  1. From 12 February 2024: for major new developments of 10 or more dwellings in England.
  2. From 2 April 2024: for non-major developments, categorised as:
  • Less than 10 dwellings on a site of 1 hectare or less; or
  • 5 hectares where the number of dwellings is unknown; or
  • In respect of commercial space, having a floor space less than 1,000 square metres or a total site area of less than 1 hectare.
  1. From late November 2024: for nationally significant infrastructure projects.

Permissions granted for applications made before 12 February 2024 are not subject to BNG.

How is a BNG of 10 per cent measured?

A BNG of 10 per cent is measured by the statutory biodiversity metric developed by The Department for Environment, Food and Rural Affairs (DEFRA). It measures biodiversity in standardised “biodiversity units”, taking into account different factors such as size, condition, location and type of the habitat.  Some local authorities are imposing a higher percentage than the statutory 10 per cent.

How can the statutory BNG percentage be achieved?

There are a number of options for developers to pursue in order to achieve the statutory BNG percentage:

  • Create it on-site within the development area (i.e. the redline planning boundary).
  • Through a mixture of either on-site measures or off-site land within the developer’s ownership or by buying offsite units on the market. It is not clear as to whether the land needs to be in a specific proximity to the development site.
  • Where the 10 per cent (or higher) BNG percentage is unachievable, developers can purchase statutory biodiversity credits from the government.
  • A combination of all three options above, but this will be dictated by the Biodiversity Gain Hierarchy, where developers will need to demonstrate they have considered the above three options in order; buying statutory biodiversity credits is the last resort.

How should BNG be incorporated into the planning process?

A Biodiversity Gain plan must be prepared to assess the natural habitats on-site before development and after development. The plan must also address how the impact on habitats can be minimised or, where harm may be caused, how this can be remedied by habitat creation or enhancement. The plan must secure maintenance for significant on-site habitat enhancements for at least 30 years after development has taken place.

The plan can either be prepared and submitted with the developer’s planning application or it will be a condition to any planning consent granted. It is important to highlight a plan must be submitted and approved prior to development commencing.

BNG will be considered throughout the planning process and local authorities will consider whether the biodiversity gain condition is capable of being successfully discharged through the imposition of conditions and agreement of section 106 planning obligations. The plan will allow the local authorities to monitor and take enforcement action if commitments are not met.

BNG exemptions

Which planning permissions are exempt from BNG?

  • Retrospective planning permissions made under section 73A of the Town and Country Planning Act 1990 (“TCPA 1990”).
  • Section 73 TCPA 1990 permissions where the original permission which the Section 73 permission relates to, was either granted before 12 February 2024, or the application for the original permission was made before 12 February 2024.
  • The approval of reserved matters for outline planning permissions is not within the scope of BNG, but the subsequent technical detailed consent (i.e. the grant of a planning permission) would be subject to BNG.

Which type of developments are exempt from BNG?

  • Until 2 April 2024, non-major developments (as detailed previously in this article).
  • Householder developments which relate to the development of an existing dwellinghouse or development within the curtilage of such dwellinghouse (permitted development).
  • A development which does not impact a priority habitat and impacts less than 25 square metres of on-site habitat or 5 metres of linear habitats such as hedgerows.
  • Self-build and custom build developments, i.e. a development which consists of no more than 9 dwellings and is carried out on a site which has an area no larger than 0.5 hectares, and is exclusively for dwellings which are self-build or custom housebuilding.
  • Urgent Crown development or other development prescribed by the Secretary of State via a development order.
  • Developments which are undertaken solely or mainly for the purpose of fulfilling, in whole or in part, the biodiversity gain condition which applies in relation to another development; and
  • Developments forming part of or ancillary to the high-speed railway transport network.

Notwithstanding these exemptions, the Government has made clear it still wants to see improvements in biodiversity. This could mean for smaller sites (such as the self-build and custom build sites), local authorities may impose a lower percentage of BNG or other “green” conditions to planning.


While the introduction of BNG is a positive step in contributing to the preservation and growth of wildlife following development, the planning legislation now imposes onerous conditions which developers will need to overcome and consider as part of their development plans. Preparation of the BNG plan and the impact of BNG on the development should be considered as early as possible, and developers should seek advice to ensure the delivery and maintenance of BNG on the sites they select to develop.

The Hamlins Real Estate team offer clients the full complement of real estate services, including commercial property, finance, litigation and construction. If you would like to find out how we can help you, please get in touch.

Biodiversity Net Gain: why everyone is going ‘wild’ for BNG

Have a question? Contact Hana

Have a question? Contact Hana


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