Achieving biodiversity net gain – the biodiversity gain hierarchy

In our recent biodiversity net gain (BNG) webinar, Harry Wright of BrightTide introduced the session in which Tim Stansfeld and Henry Parkinson of the Langley Abbey Environment project discussed all aspects of BNG, including the biodiversity gain hierarchy. 

The hierarchy stems from Article 37A of the Town and Country Planning (Development Management Procedure) (England) Order 2015 and requires, in order of priority:

  • first, in relation to on-site habitats which have a medium, high and very high distinctiveness, the avoidance of adverse effects from the development and, if they cannot be avoided, the mitigation of those effects
  • following this principle, the hierarchy can be broken down into three main means to achieve 10% BNG:
  • Enhancing or creating new habitat on site
  • If this is justifiably not achievable, delivering off-site gains or purchasing off-site biodiversity units, and registering these on the biodiversity gains site register
  • If such off-site gains are justifiably not achievable, purchasing statutory biodiversity credits

The cost of statutory biodiversity credits is marked up to prevent them undercutting the off-site market.  Accordingly, purchasing statutory biodiversity credits is intended to be the most expensive way for developers and landowners to achieve a 10% biodiversity net gain and is the method of last resort.

Whilst creating or enhancing a habitat on-site is at the top of the hierarchy, it is not a mandatory requirement. Landowners and developers will need to take a pragmatic approach as to how to create and maintain their 10% net gain.

To determine the best option available for each individual development, landowners and/or developers will need to take into account:

  • the size of their site
  • the location of their site
  • the baseline biodiversity value of the development site
  • the cost effectiveness of creating and maintaining habitats on the development site

Sites with a lower baseline biodiversity value will require less enhancement to achieve a 10% net gain than a site with a higher starting baseline value.

However, if your habitat creation on-site starts from a low biodiversity baseline level, it is potentially less likely to succeed and flourish during the 30-year maintenance period. In these circumstances, it may be more cost-effective in the long-term to the landowner and/or developer to purchase off-site units.

As discussed in our recent webinar, whilst every development site is unique, it could be approaching six times more cost effective to purchase off-site biodiversity units compared to creating and maintaining a biodiverse habitat on-site for the required duration.

As individual development sites can often only deliver small pockets of habitat creation, the discussions from the webinar indicate that landowners may well benefit from looking to their neighbouring land to deliver larger, combined and integrated habitats. Purchasing biodiversity units from off-site locations will also take away some of the obligations, responsibilities and risks associated with on-site delivery for landowners and developers.

Purchasing biodiversity units off-site could also mean local planning authorities have fewer overall sites to monitor, rather than numerous pockets of smaller disparate habitat sites.


The BNG requirements are an important part of the overall efforts to restore nature and enhance habitation in an effort to end the decline in species populations, to lock away carbon and to mitigate climate risk and damage.

In using off-site location opportunities to fulfil BNG requirements, developers could have greater scope to maximise their available development site space, whilst minimising their long-term administrative maintenance burden. The key, though, is to ensure the hierarchy is followed, and the approach developers’ wish to pursue is justified. We do, though, expect that a pragmatic and practical approach to fulfilling the BNG requirements will become the industry standard, to balance the benefits of BNG delivery alongside enabling sustainable development projects to come forwards.

Related biodiversity items

Understanding biodiversity net gain (BNG) - Tim Stansfeld, Legal Director

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