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Biodiversity Net Gain Condition Assessment: All you need to know

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Biodiversity net gain is a concept in conservation biology that refers to the net increase in biodiversity that results from a development project. This means that the project should not only avoid negative impacts on habitats and biodiversity, but should also actively contribute to increasing the diversity of species and habitats in the area, ultimately delivering biodiversity net gain.

Biodiversity net gain can be achieved through various means such as creating new habitats, restoring degraded ones, or translocating species to new locations. The goal of biodiversity net gain is to ensure that development projects do not result in a net loss of biodiversity, and ideally lead to an overall improvement in the health and diversity of ecosystems.

By complying with the guidelines of biodiversity within their development plans, developers, project and land managers should have more chance of their planning permissions being granted, as this is up to each local planning authority to determine.

Our team of Ecologists are highly experienced with the rules and guidance surrounding biodiversity and can assist clients all across England and Wales. If you are in need of advice or an expert Ecologist to help you with biodiversity net gain requirements, planning policies and decisions then please don’t hesitate to get in touch today.

What is a Biodiversity Net Gain Condition Assessment?

A biodiversity net gain condition assessment is a process used to evaluate the potential impact of a development project on biodiversity and to determine if the project will result in delivering net gain or loss of biodiversity. The assessment typically involves a comprehensive survey of the site and its surrounding area to identify the existing species and habitats present, as well as an analysis of the potential impacts of the proposed development on these species and habitats.

The assessment also includes an evaluation of the proposed measures to mitigate negative impacts and enhance biodiversity, such as creating new habitats, restoring degraded ones, or translocating species to new locations. Based on the results of the assessment, recommendations may be made to improve the project design and mitigate negative impacts on biodiversity. The assessment will also include a calculation of the net gain or loss of biodiversity, based on the difference between the baseline conditions of the site and the expected conditions after the development project is completed.

Biodiversity net gain condition assessment is a requirement for most of the development projects as a mean of demonstrating compliance with planning policies and regulations.

When will biodiversity net gain be mandatory?

Local planning authorities require all permissions they grant to achieve at least 10%  biodiversity following the Environment Act 2021. A provision for secondary legislation has been put into place from the act, which will set a date in which the mandate will come into force. Currently, the mandate is expected to come into force towards the end of 2023.

The Environment Act 2021 allows a transitional two-year period for local authorities to get their policies and processes smoothly in place before BNG becomes mandatory in 2023.

The current national policy in England, The National Planning Policy Framework (NPPF) Paragraph 179 states:

  • “To protect and enhance biodiversity and geodiversity, plans should:
  • “Identify and pursue opportunities for securing measurable net gains for biodiversity.”

Paragraph 180 states:

  • “When determining planning applications, local planning authorities should apply the following principles: opportunities to improve biodiversity in and around developments should be integrated as part of their design, especially where this can secure measurable net gains for biodiversity”

Many Local Planning Authorities have already been requesting the assessment for BNG for a number of years already, and many of them are beginning to amend local developers’ processes to ensure they meet the set standards as part of the local policy.

The Act will require the key points:

  • Developers must deliver BNG at a minimum of 10% through their schemes. This will be measured through a metric, currently Biodiversity Metric 4.0. This tool can help to identify your biodiversity unit score and translate it into the standards of local planning authorities.
  • A developer will need to demonstrate how biodiversity gain will be delivered on developed land. This will be demonstrated through the production of detailed Landscape Planting Schemes, Landscape Management Plans and Monitoring assessments for on and/or off-site.
  • A mitigation hierarchy is to be followed and demonstrated to avoid, minimise or compensate. If it is not possible to compensate on the development site, then offsetting on other designated sites will be required elsewhere.
  • Developers will have to guarantee the biodiversity gain is maintained for at least 30 years (as outlined in Landscape Management Plans).
  • New “local nature recovery strategies” will be prepared to geographically cover England by “responsible authorities”. This will encourage habitat creation and enhancement in the right places.
  • Conservation covenants will be a mechanism used to deliver this (this approach is in preparation by Defra and Natural England).
  • A national register of land used for biodiversity gain will be established. This will involve setting up a new biodiversity credits market.
  • Metrics are only concerned with habitats and do not take protected species into consideration.
  • Other ecological legislation and policies still apply.


The Environment Bill ultimately endeavours to encourage developers to think about the mandatory biodiversity net gain before and during the acquisition of land to avoid changing plans and calculation further down the line once processes have already begun. Having to adapt an on-going development to meet BNG will lead to delays and financial loss to name but a few problems they may encounter.

How can we help?

If you require more information regarding biodiversity net gain condition assessments then our team at Collington Winter will be more than capable to assist you. Achieving net gain for biodiversity through development is something that we are qualified and experienced in. Plus, we can offer advice on planning projects.

At Collington Winter, our team of ecologists are experts in the field of biodiversity net gain and can keep you up to date with new and changing legislation. As regulations can vary across local authorities it is important to instruct a qualified ecologist to ensure you are following the correct rules.

Please get in touch if you would like further information about Biodiversity Net Gain, or biodiversity net gain condition assessments. You can email our Ecology Director, Olivia Collington, at or use the form below and a member of our team will be in touch with you.

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