Collington Winter Environmental

Biodiversity Net Gain Assessment: When are they required?

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What is a biodiversity net gain assessment?


Following the introduction of The Environment Act 2021, developers on all new development projects should aim to protect ecosystems and habitats on site. A biodiversity net gain assessment should be carried out as early as possible within the development planning stages to identify and mitigate any potential habitat loss on the development site.

Mandatory biodiversity net gain will be introduced following the 2 year transition period in 2023 which will place a responsibility on developers to consider the environmental impact of a development in terms of biodiversity. The introduction of net gains for biodiversity also aims to ensure that the environment is left in a better state than before the development was completed. 

Why is a biodiversity net gain assessment required for developments?

The Environment Bill gained royal assent in 2021, and under The Environment act 2021, all developments will need to ensure there is at least a 10% net gain to biodiversity, post development. This net gain will be measured through Metric 4.0.  

Following a two year transition period, biodiversity net gain will become mandatory in 2023. The Environment Act act will introduce the requirement to deliver biodiversity net gain for all developments in England.

In addition to this, the current national policy in England, The National Planning Policy Framework (NPPF) Paragraph 179 states:

“To protect and enhance biodiversity and geodiversity, plans should:

  1. b) … identify and pursue opportunities for securing measurable net gains for biodiversity.”

As a result of these regulations, most planning applications for developments will be unable to proceed until local planning authorities are satisfied that the required biodiversity standards have been met.

Providing Biodiversity Net Gain assessments alongside methods for achieving Biodiversity Net Gain within a development’s proposal will soon become essential in order to receive the appropriate planning permission.

Calculating Biodiversity Net Gain

A biodiversity net gain assessment will use some sort of metric to assess each habitat type. Natural England’s Biodiversity metric 4.0 is currently the most widely used metric which is used to calculate biodiversity unit scores and translate them into the standards of the local authority.

For each habitat, the metric will assess:

  • The condition and quality of the habitat
  • The connectivity of the habitat, i.e., how well connected the habitat is to other similar habitats
  • The strategic significance of the habitat

The government website provides a biodiversity metric 4.0 calculation tool that can help developments to determine their biodiversity unit score under the standards of their local planning authority.

Biodiversity Net Gain Plans

In order to obtain planning permission for a development, developers must be able to prove that they are taking the correct measures to increase biodiversity net gain. One of the initial steps in this process is to contact an experienced ecologist to create and develop a biodiversity net gain plan.

Depending on the ecologist’s findings within a biodiversity net gain assessment, the biodiversity net gain plan will help to determine the natural elements that could potentially be at risk as a result of the proposed development project, as well as any mitigation methods which should be used to prevent damage.

How can our team assist?

Our team have assisted numerous clients over the years, including policy guidance for biodiversity gain in England. It is important to note that BNG varies across each Local Planning Authority.

There are three stages of using a biodiversity net gain assessment, and we assist our clients during the very early stages of development, including promotions and land purchases. We are happy to complete an informal initial assessment for sites of interest. This helps our clients understand the probable implications and costings of Biodiversity Net Gain from the offset.

Project Feasibility

  • Identifying implications for potential development projects.
  • Audits of land for biodiversity gain capacity at the land acquisition stage.
  • Providing advice on options for delivery of biodiversity gain on and off-site or potential unit costs to the Local Planning Authorities.


Assessment and design

  • Baseline survey and habitat condition assessment – to provide data for the biodiversity metric (completed as part of a Preliminary Ecological Appraisal).
  • Detailed design-phase input: aim to retain the highest valued ecological features and scope for creating or enhancing habitats.
  • Combining green infrastructure, SANG and habitat provision.
  • GIS expertise: managing metric data and supporting calculations.

Planning permission and delivery

  • Planning conditions: working with a project team (especially landscape teams) with the aim to provide feasible, proportionate and practical final designs and management.
  • Preparing long-term site management plans (or consult with Landscape Architects) and advising on future monitoring commitments.
  • If offsetting is required, we will liaise with local authorities, conservation organisations, and other third parties for agreeing the delivery of biodiversity gain.

Please get in touch if you would like further information about Biodiversity Net Gain or Landscape Management Plans. We are happy to offer free CPD sessions on the Biodiversity Net Gain Principles and how we can help your schemes achieve this.


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