Biodiversity net gain (BNG) is an approach to development. It makes sure that habitats for wildlife are left in a measurably better state than they were before the development.
In England, BNG is mandatory under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021).
Policy PL9 of the Harlow Local Plan also requires development to contribute and enhance biodiversity or geodiversity assets, to ensure a net gain in biodiversity.
Developers must deliver a BNG of 10%, unless they are exempt. This means a development will result in more or better quality natural habitat than there was before development.
BNG does not change the existing legal protections for important habitats and wildlife species.
Measuring biodiversity
You must use the statutory (official) metric to measure the biodiversity value of your development site. It measures all types of habitat, including grassland, hedgerows, lakes, woodland, watercourses such as rivers and streams.
The metric measures the biodiversity value of habitats by calculating the number of biodiversity units. It calculates:
- how many units a habitat contains before development takes place
- how many units are needed to replace the units of habitat lost and to achieve 10% BNG, through the creation or enhancement of habitat
The formula takes different factors into account, including the habitat’s size, condition, strategic significance and type. For created or enhanced habitats, the formula also takes account of:
- difficulty of creation or enhancement
- the time it takes a habitat to reach its target condition
- distance from the habitat loss
A competent person such as an ecologist should complete the metric.
You can choose to use a simpler version of the metric tool, called the small sites metric, if your development meets the criteria to do so. A qualified ecologist does not need to complete this.
You can find more details on the metric, including a user guide on GOV.UK. You can also find the latest statutory metric.
Achieving BNG
There are 3 ways a developer can achieve BNG.
- They can create biodiversity on-site (within the red line boundary of a development site).
- If developers cannot achieve all of their BNG on-site, they can deliver through a mixture of on-site and off-site. Developers can either make off-site biodiversity gains on their own land outside the development site, or buy off-site biodiversity units on the market.
- If developers cannot achieve on-site or off-site BNG, they must buy statutory biodiversity credits from the government. This should be a last resort. The government will use the revenue to invest in habitat creation in England.
Developers can combine all 3 options but must follow the steps in order. This order of steps is called the biodiversity gain hierarchy.
Submitting a planning application
If you consider the application to be exempt from BNG, then this must be justified in the planning application.
If your application is not exempt, then you must submit the following information with your application:
- the completed biodiversity metric tool showing the onsite habit score as of the date of the application or for an earlier proposed date with justification
- if any habitat degradation has occurred, the completed metric for before the degradation occurred
- the score in biodiversity units
- the publication date of the version of the metric being used
- if any degradation has occurred, a statement that it has occurred, when it started and any evidence for the date it started and the score before the degradation
- a description of any irreplaceable habitat - defined in The Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024 Schedule 2 - within the red line boundary as of the metric calculation date
- a scale plan (showing north) of the onsite habitat used in the calculations and any irreplaceable habitat
In addition to the above, we strongly recommend that you submit a draft biodiversity gain plan providing information as to how the development has addressed the biodiversity mitigation hierarchy and how it is intending to meet the BNG objectives.
This will also help determine whether any section 106 planning obligations are required to secure either significant onsite habitat enhancements or offsite gains for the development.
After planning permission is secured
Submitting a biodiversity gain plan
A BNG condition will be included within the decision notice. You must submit a biodiversity gain plan to discharge that condition. This must include:
- information about the steps taken or to be taken to minimise the adverse effect of the development on the biodiversity of the onsite habitat and any other habitat
- the pre-development biodiversity value of the onsite habitat
- the post-development biodiversity value of the onsite habitat
- any registered off-site biodiversity gain allocated to the development and the biodiversity
- any biodiversity credits purchased for the development
You can use the government's biodiversity gain plan template.
For phased developments, you must submit an overall biodiversity gain plan before works begin, as well as phased biodiversity gain plans alongside each subsequent phase.
Legal agreements and conservation covenants
For significant on-site habitat enhancements, a legal agreement or condition will be required. On-site gains must last 30 years, and non-significant enhancements do not need to form part of the agreement unless they contribute to locally important species or ecological networks.
To buy or sell off-site gains, a legal agreement is required. The legal agreement for off-site gains must last for at least 30 years from the date you finish the habitat enhancement.
Legal agreements can be made through a planning obligation (or possibly a condition) with the council or through a conservation covenant with a responsible body.
Monitoring BNG habitat enhancements
The Environment Act states that habitats should be secured for a minimum of 30 years and managed and monitored appropriately.
The government encourages use of a habitat management and monitoring plan (HMMP) to capture management and monitoring information for significant on-site enhancements and off-site gains.
More detailed guidance on BNG can be found at GOV.UK.