Biodiversity net gain now and in the future

Page updated 2 October 2023

This page is part of our online resource on biodiversity net gain for local authorities. It summarises biodiversity net gain policy and guidance available now, as well as forthcoming requirements for mandatory biodiversity net gain through the Environment Act 2021. The Biodiversity net gain for local authorities page provides an introduction to the topic.

Biodiversity net gain now

National policy sets out that planning should provide biodiversity net gains where possible. National Planning Policy Framework (NPPF) Paragraphs 170(d), 174(b) and 175(d) refer to this policy requirement and the Natural Environment Planning Practice Guidance (PPG) provides further explanation on how this should be done. Delivering net gain is also referred to in the National Infrastructure Commission's Design Principles, National Policy Statements and the National design guide.

The Government's 25 Year Environment Plan sets out the aspiration to mainstream biodiversity net gain in the planning system and move towards approaches that integrate natural capital benefits.

The Biodiversity Metric is designed to provide ecologists, developers, planners and other interested parties with a means of assessing changes in biodiversity value (losses or gains) brought about by development or changes in land management. The metric is a habitat based approach to determining a proxy biodiversity value. A Small Sites Metric, a beta version designed to simplify the process of calculating biodiversity net gain on smaller development sites, is also available. A recording of the webinar launching these tools is available on YouTube

An updated Biodiversity Metric 4.0 was published in March 2023. This is an update to version 3.1 launched in April 2022: a summary of changes made in version 3.1 is available on the Biodiversity Metric webpage.

We hosted an introduction to the BNG Metric and Checklist for LPA planning officers for Natural England on 6 July 2023. The session was principally focused on the BNG Metric and using the checklist in the process of validation of applications. The recording and slides of the event are available. We hosted intermediate level training from Natural England on Biodiversity Metric 4.0 in September 2023.

CIEEM, IEMA and CIRIA have set out Good Practice Principles for Development and an associated Practical Guide and Case Studies for biodiversity net gain.

There is now a British Standard on biodiversity net gain and development projects: BS 8683:2021 Process for designing and implementing Biodiversity Net Gain.  The standard specifies requirements for a process to design and implement BNG for development projects. It doesn’t cover the actual delivery of BNG, but provides a framework to demonstrate that a project has followed a process based on UK-wide good practice. Find out more from the British Standards Institute (BSI) webinar replay of 21 May 2021. BSI have also produced a Little Book of Biodiversity Net Gain to accompany the British Standard.

CIEEM have also published Biodiversity Net Gain Report and Audit Templates that provide a framework for writing reports for projects that are aiming to achieve BNG. The templates set out a suggested structure and content for reports specifically produced in relation to BNG assessments.

This article in LGA's first magazine for councillors highlights why councils should start thinking about and planning for biodiversity net gain now. Defra have also set out 10 actions local planning authorities can take to prepare for Biodiversity Net Gain (BNG).

Mandatory BNG and the Environment Act

The Government announced it would mandate net gains for biodiversity in the Environment Bill in the 2019 Spring Statement. This followed a consultation on net gain from December 2018. Defra's response to the consultation was published in July 2019. An impact assessment on biodiversity net gain and Local Nature Recovery Strategies was published in late 2019.

The Environment Bill received Royal Assent on 9 November 2021, meaning it is now an Act of Parliament: World-leading Environment Act becomes law - GOV.UK ( This blog of 20 July 2023 summarises what’s happened and what’s coming next in terms of BNG policies and framework and this Government press release from 27 September 2023 outlines the timetable for mandatory BNG.

Mandatory biodiversity net gain as set out in the Environment Act applies in England only by amending the Town & Country Planning Act (TCPA) and is likely to become law in January 2024 with key statutory instruments published in November 2023. The Act sets out the following key components to mandatory BNG:

  • Minimum 10% gain required calculated using Biodiversity Metric & approval of net gain plan
  • Habitat secured for at least 30 years via obligations/ conservation covenant
  • Habitat can be delivered on-site, off-site or via statutory biodiversity credits
  • There will be a national register for net gain delivery sites
  • The mitigation hierarchy still applies of avoidance, mitigation and compensation for biodiversity loss
  • Will also apply to Nationally Significant Infrastructure Projects (NSIPs)
  • Does not apply to marine development
  • Does not change existing legal environmental and wildlife protections

PAS ran events on Biodiversity Net Gain and the Environment Bill in Summer 2021. You can access the slides from the workshops here for an overview of the situation with biodiversity net gain and the Environment Bill in Summer 2020 and to see what we discussed with attendees. A summary of the outputs from the workshops is available, including what local authorities are doing now on biodiversity net gain (BNG) and what they need to enable them to be ready for mandatory BNG.

The Government published a consultation on Biodiversity Net Gain Regulations and Implementation on 11 January 2022. The consultation sets out proposals on the detail of implementation of mandatory BNG and closed on 5 April 2022. 

In February and March 2022, PAS ran events for local authorities on the consultation. The events were intended to help LPAs understand what the consultation covered and how best to respond. We ran overview events and deep-dive discussion sessions on key topics. Slides and recordings of the events plus a summary of what we heard are available on our Biodiversity Net Gain Consultation events webpage.

We ran events on biodiversity net gain and nature recovery in Autumn 2022 and slides and recordings, plus a summary of what we learnt is available on our events page.

Government published its response to the 2022 consultation on 21 February 2023. This is accompanied by some guidance on biodiversity net gain with more on its way as well as the secondary legislation that will implement mandatory BNG.


The timelines for introduction of mandatory BNG are dependent on a number of factors. The below is our current understanding of the likely timetable towards mandatory BNG.

Autumn 2021:

  • 9 Nov - Environment Bill gets Royal Assent - now the Environment Act

Winter 2021/22:

Spring/Summer 2022: