What is the Biodiversity Net Gain regime?

The new Biodiversity Net Gain regime is a requirement on all developments to provide enhancements in biodiversity.

Who does BNG apply to?

The first stage of the Biodiversity Net Gain (BNG) regime (introduced by the Environment Act 2021) will, save for the Exemptions, affect all planning applications submitted on or after 12 February 2024.

BNG will not apply to a section 73 planning permission where the original planning permission was either applied for or the permission granted before 12 February 2024.

What are the Exemptions?

There are exemptions for:

  • De minimis developments which:
    • don't impact an onsite priority habitat,
    • impact less than 25 square metres of onsite habitat,
    • less than 5 metres in length of onsite linear habitat
  • Householder applications
  • Applications for self-build and custom build developments of:
    • < 9 dwellings, and
    • < 0.5 hectares, and
    • of self-build or custom-build dwellings only
  • High speed rail developments
  • Developments undertaken solely or mainly to fulfil the biodiversity gain planning condition which applies to another development .

There are also temporary exemptions, which will have their own regimes in the future, for:

  • Small sites until April 2024
  • Nationally Significant Infrastructure Projects until November 2025.

There are slightly different regimes for Irreplaceable Habitat and Phased Schemes. Look out for other blogs on these points.  

How does the BNG regime work?

The Environment Act 2021 imposes a condition on all (non-exempt) planning permissions that you cannot commence development until a biodiversity gain plan (BGP) for the development has been approved by the local planning authority. 

A baseline BNG value calculation showing the pre-development biodiversity value of the site will need to be submitted with the planning application along with information about how the developers intend to meet the BNG requirement.

If planning consent is granted, a BGP setting out the BNG strategy must then be submitted to the local planning authority for approval.

To be approved, the BGP must demonstrate a 10% biodiversity net gain against the pre-development biodiversity value and show that these enhancements will be maintained for 30 years from the completion of the enhancements.

How is Biodiversity value calculated?

This is calculated by using the Biodiversity Metric published by Natural England. This calculates a biodiversity value expressed in Biodiversity Units. An increase in the number of Biodiversity Units shows an increase in Biodiversity value.

How can you achieve the 10% biodiversity net gain?

You can use one or a combination of the following three options:

  • Provide onsite enhancements
  • Provide offsite enhancements that are secured by Section 106 Agreement or conservation covenant (commonly referred to as “offsite” units)
  • Purchase statutory credits (each “statutory credit” will be worth half a biodiversity unit).

You must demonstrate:

  • Total number of onsite units
  • Total number of offsite units
  • Total number of statutory credits units

To equal a 10% increase in total number of pre-development onsite units.

You must prioritise onsite enhancements and mitigations, over offsite and statutory credits where possible.

If a developer is unable to achieve 10% BNG onsite, they can look to offsite measures with purchasing statutory credits being a last resort. However, statutory credits are highly discouraged as shown by their high price and the requirement on developers to provide evidence why they cannot use onsite or offsite enhancements to achieve the 10%.

One thing to watch out for?

There are different categories of biodiversity units:

  • Area units (e.g. grass meadows and forests)
  • Linear units (e.g. hedgerows)
  • Water units (e.g. lakes)

If you have a more than one of the above onsite pre-development, you will need to show a 10% gain in each category individually – you cannot offset loss in one category with greater enhancements in another!


Our content explained

Every piece of content we create is correct on the date it’s published but please don’t rely on it as legal advice. If you’d like to speak to us about your own legal requirements, please contact one of our expert lawyers.

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