Updated by Nikki O’Hagan, 12th April 2024

An introduction to Biodiversity Net Gain

Biodiversity Net Gain (BNG) is a new legal requirement affecting most types of planning applications in England.

The intention of the new legislation is to ensure the biodiversity value of development sites is measurably improved as a result of development. To achieve this, the law requires most planning applications to demonstrate a minimum 10% gain for biodiversity.

This new legal requirement was introduced for major sites on the 12th of February 2024. Small sites were given an exemption until the 2nd of April 2024. Since this date, the requirement has applied to small sites as well as major.

Some other, generally minor developments remain exempt for the foreseeable future.

What developments are exempt?

At the time of writing, the following developments are exempt from the legal BNG requirement:

  • Householder developments. These are developments that affect an existing house or its grounds, including domestic extensions, domestic outbuildings and domestic enclosures (fences, gates etc.)
  • Certain self-build and custom housebuilding applications. These are applications for new dwellings that are to be built by or on behalf of an individual (or collection of individuals) for occupation by that individual. The exemption only applies where:
    • The development consists of no more than 9 dwellings
    • The development site has an area of no more than 0.5 hectares
    • All dwellings in the application are of the self-build or custom build type

There is also a de minimis exemption. This means that development that meets both of the following two tests is also exempt from the BNG requirement:

  1. The development does not impact an onsite “priority habitat”
  2. The development impacts:
    • Less than 25 square metres of onsite habitat that has a “biodiversity value” greater than zero
    • Less than 5 metres in length of onsite “linear habitat”.

In some local areas, Councils have adopted their own Biodiversity Net Gain planning policies that apply to sites and developments that would otherwise be exempt from the legal BNG requirement. If this is the case in your area, you will be expected to comply with the local BNG policy.

Definition of key terms

  • Priority habitat – these are specified habitats of principal importance to UK biodiversity. The list of priority habitats includes arable field margins, bogs, hedgerows, woodland, traditional orchards, heathland, reedbeds, meadows, rivers, ponds and more.
  • Biodiversity value – biodiversity value is to be measured using the government’s statutory biodiversity metric tool. The metric takes into account the size, condition, strategic significance and type of on-site habitats. If a site has a biodiversity value of zero that means it has no biodiversity value at all. This would likely apply, for example, to a site covered throughout by tarmac, concrete or traditional buildings
  • Linear habitat – hedgerow and watercourse habitats.

There are a few more exemptions but they are unlikely to affect the average developer or site owner.

What do I need to do about Biodiversity Net Gain?


If you believe your development is exempt, you must include a statement explaining why it is exempt alongside your planning application.

Not exempt

If your development is not exempt, you are required by law to submit a Biodiversity Gain Plan before you commence development. You must not commence development until the plan is approved. The plan will demonstrate how the minimum 10% biodiversity gain will be achieved. The government has produced a Biodiversity Gain Plan template which is available online.

In addition, you must submit a biodiversity metric calculation alongside your planning application. This must be calculated using the government’s statutory biodiversity metric tool which is also available online. The metric assessment should be completed by a competent person. Although you do not necessarily need to share your Biodiversity Gain Plan with the council at this stage, you will likely require a draft version in order to complete the metric assessment.

Our advice is to submit your draft Biodiversity Gain Plan alongside your planning application as you may receive valuable comments on its contents that will assist you to refine it. This will increase the chances of your final plan being approved the first time around.

Finally, you will need to submit a plan (drawing) that accurately shows the type and extent of all existing site habitats. This will require a site walkover.

How do I achieve a 10% gain for biodiversity?

Option 1 – onsite

The government’s expectation is that the full 10% gain will be delivered within the boundaries of the development site wherever possible. This will be achieved via the provision of new or enhanced green infrastructure. This includes things like woodlands, hedgerows, meadows, ponds and any other landscape features that provide wildlife habitats. You can extend or improve an existing habitat or create a whole new one.

The land owner will be legally responsible for both creating and maintaining the new habitat/s for a minimum period of 30 years.

If the 10% gain cannot be delivered onsite, there are two remaining options. However, you must be able to clearly justify why the net gain cannot be achieved onsite. If you are able to deliver less than the 10% gain onsite then you should do so and use the remaining options to make up the shortfall.

Option 2 – offsite

If you are unable to deliver the full 10% gain onsite, then the next best option is to deliver the gain offsite. This means creating new or enhanced habitats on land outside of the development site. This could be on adjacent land but the site can be anywhere in England. The biodiversity metric does look more favourably on offsite gains that are located close to the development site, however.

You can either make your own offsite gain on land in your ownership or you can buy offsite “units” from a land manager. There are already many companies in England offering these units for sale.

If you choose to deliver the gain on your own land, you will be legally responsible for maintaining the new habitat/s for a minimum period of 30 years. If you purchase your offsite units from a land manager, they will be legally responsible for maintaining the habitat/s over this period.

Option 3 – statutory biodiversity credits

Buying statutory credits is a last resort. It is only an option for developers who cannot achieve onsite or offsite biodiversity net gain. Developers who wish to buy statutory credits must prove why they cannot achieve the 10% gain using one or both of the preferred options outlined above.

Developers can use a combination of the 3 options but must prioritise options 1 and 2, in order. If, for example, a developer is able to achieve a 5% onsite gain and a 3% offsite gain then they should only purchase statutory credits to make up the remaining 2%.

To purchase statutory credits, you must submit an application to Natural England. Natural England aims to consider your application within 8 weeks. Any credits you purchase will be non-refundable.

Follow the link below to find out more about the application process.

How can Planning Direct assist me?

Planning Direct can assist you with all aspects of Biodiversity Net Gain. We are able to produce most BNG documents in-house. For larger and more complex developments, however, some BNG documents will be produced by one of our trusted, ecology partners.

Planning Direct offers comprehensive planning application services at competitive rates. If you choose this service, we can ensure your BNG strategy is considered and incorporated from the earliest design stages to avoid delays and additional, unexpected costs further down the line.

If your development is affected by BNG, contact us today to find out how we can assist you. Our initial advice is always free of charge.

Prefer to go straight to the source? The government has issued various guidance documents relating to Biodiversity Net Gain. Follow the link below to access an online copy of their primary guidance.

Back to top