Biodiversity Net Gain

What is biodiversity net gain?

The BNG approach involves assessing proposed development sites prior to planning permission being sought, so that the design and a long-term management plan can create and maintain BNG gains of 10% over 30 years.  BNG responsibilities not only impact upon new developments, but also on the long-term management of green spaces. This can directly impact your asset strategy and any ground maintenance contracts.

When does it apply?

Ensuring a BNG of at least 10% has been mandatory for new development since early 2024. The date that the requirement came into effect depends on the scale of the development:

• Feb 12th 2024 for major planning applications
• April 2nd 2024 for minor planning applications

Planning permissions received before those dates should not have to comply with national BNG requirements. However, you should check with your local planning office to be certain about BNG and your development, as they may have adopted local policies that came into effect before the dates above.

Even if the planning permission was granted after the dates above, the development could be exempt if:

• It is a variation of existing planning permission
• A development that does not impact a priority habitat and impacts less than: 

• 25 square metres (5m by 5m) of on-site habitat 
• 5 metres of on-site linear habitats such as hedgerows

How is BNG measured?

There is a statutory biodiversity metric tool. This tool needs to be used by a competent person, described as someone with the appropriate skills and knowledge to complete and review biodiversity metric calculations. Use of the tool should align with British Standard 8683 process for designing and implementing BNG.  

The site will contain a certain number of BNG units. This will be impacted by:

• Size
• Quality of the habitat
• Location
• Type

The more special the site, for its habitat, the greater number of BNG units it will score. For example a brownfield site in a city will score considerably less than a similar sized area of land in the Peak District National Park. A small area in a National Park with priority habitats could score higher than a large city centre area.

How do I find out what the current BNG score is?

Before you can start any work, you need to understand the baseline for the land you want to develop on.  This can be done in a number of ways:
An ecologist or suitably experienced and qualified assessor can survey the site using the biodiversity metric tool to measure how many biodiversity units there are
Software systems, which use data from a variety of sources and artificial intelligence, to measure the number of biodiversity units on a site

Both approaches will create a baseline BNG score. As the BNG target means the overall development must result in a 10% increase on this, any BNG reduction from the development must be calculated before you can understand how much needs to be created. This is shown in the following example:

How do you deliver 10% BNG?

The 10% BNG can often be delivered in the landscaping of a development and surrounding area. Planting new trees and shrubs etc., increases biodiversity and can provide new habitats. However, if you are working with a constrained site or a site that is already very biodiverse, achieving 10% BNG can be more challenging. In these situations you have two options:

1. Achieve all or part of your BNG on a different site locally. This is known as off-site BNG and can be the result of planting or other landscaping work on land you own. You can also work in partnership with a local landowner; many wildlife trusts develop their nature sites to achieve a developer’s 10% BNG. They also commit to maintaining the BNG for the 30 years required
2. If you cannot create the 10% BNG, either yourself or by off-siting, there is an option to purchase BNG credits from the government. At the time of writing, this started at £40,000 per unit

Who’s responsible for the BNG and for how long?

Responsibility for the creation and 30-year maintenance of BNG needs to be considered at an early stage. This could be as new housing is developed (if you are the developer) or, if you are purchasing or taking over ownership of properties, have a BNG planning requirement. This is because the various possible management arrangements have different implications:

• The developer may deliver the BNG landscaping, but will often not take on any long-term maintenance of the BNG
• Any existing maintenance agreement may have been contracted to another organisation to upkeep. For example, this could be a local wildlife trust that was contracted to manage the maintenance of on or off-site BNG
• A landlord may have the responsibility for the BNG. If you’re purchasing new homes, you need to understand this and any implications
• The BNG has to remain for a period of 30 years from the completion date. This means ensuring that the biodiversity that created the 10% remains and no other biodiversity is lost from that site. For the landlord, this means keeping a record of the BNG plan needs to be kept for future years, so that it can inform future asset strategy.  

Grounds maintenance contracts

Each year that the BNG plan is in place the grounds maintenance contractor must maintain the BNG plan for that site. The planting that was done for the site must remain, being replaced as required to ensure the BNG is maintained. Any loss of biodiversity from that site, either whether created or maintained by the development, must remain. This needs to be embedded in your grounds maintenance contracts.

New developments

Land that has been used to create the BNG cannot be developed on for the period of the BNG plan being in place.

What happens if the BNG plan is not maintained?

If the BNG plan isn’t maintained you may in breach of planning conditions, obligations and legal agreements. In this situation the planning authority can take enforcement action against the responsible organisation.

What should I be thinking about as a landlord?

• The developers and the organisations doing any new build developments should have a clear understanding of what they need to do for BNG as part of the planning and development process. However, as a landlord there are some things that you can do:
• Ensure you have outdoor spaces in your asset database, as well as an understanding of each space’s biodiversity. This will help understand the potential for off-siting your BNG on land you own but aren’t developing
• Consider how to ensure all BNG plans are managed in any grounds maintenance contracts
• In the decision-making process for selling any land, consider if you have any forthcoming developments where there is a risk you may need to off-site your BNG. Buying BNG credits is expensive and may cost more than the income raised from selling the land
• Keep records of who is responsible for maintaining the BNG. As stated above, this could be the landowner, the developer or another organisation such as a wildlife trust
• If you’re purchasing new properties or land, ask if there a BNG responsibility on that land. 
• Ensure the long-term management plan for any BNG is available to those managing the site, such as asset managers, development managers and maintenance contractors

More information can be found on the govt website, Understanding biodiversity net gain - GOV.UK (www.gov.uk).