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Industry good practice principles for biodiversity net gain requires following the ‘mitigation hierarchy’ to avoid and then minimise impacts on biodiversity and then achieve gains by the creation or restoration of habitats on the development site, or outside of it if this is not possible (referred to as offsetting). Gains should be made with respect to species composition, habitat structure, the functioning of ecosystems and cultural values associated with biodiversity. A metric originally developed as part of the Defra 2012–2014 Biodiversity Offsetting pilot programme is the means by which quantitative estimates of the impacts on biodiversity and the subsequent gains can be derived (a revised version of the metric is currently being refined in consultation with stakeholders). The habitats on a development site are mapped, and their condition and distinctiveness (attributes intended to reflect the value of the biodiversity present) are scored with the metric to derive biodiversity ‘units’. Developers will be required to gain more biodiversity units than are initially present at the development site.

However, relying on development to fund future biodiversity increases differs markedly from previous conservation approaches. Controversies also exist in relation to the use of offsetting, which aims to increase biodiversity in another location and re-allocates the stock of biodiversity resources across time (as gains in biodiversity may take decades to accrue). Whether net gains are achieved will also depend on governance arrangements, including the rules, policies and institutions implementing the approach, and the resources available to local planning authorities to do this. In the longer term, the concept will be expanded to cover a wider set of benefits delivered by natural habitats, such as flood protection and improved water quality, with a wider ‘eco-metric’ currently being developed.

This POSTbrief summarises the net gain and previous no net loss approaches, the mitigation hierarchy and biodiversity offsetting as well as the ethical and social concerns, and the governance and technical challenges involved. 


POSTnotes are based on literature reviews and interviews with a range of stakeholders, and are externally peer reviewed. POST would like to thank interviewees and peer reviewers for kindly giving up their time during the preparation of this briefing, including:

  • Dr Joseph Bull, Durrell Institute of Conservation and Ecology, University of Kent*
  • Sophus zu Ermgassen, Durrell Institute of Conservation and Ecology, University of Kent
  • Dr Julia Baker, Interdisciplinary Centre for Conservation Science, University of Oxford and Balfour Beatty*
  • Dr Alison Smith, Environmental Change Institute, University of Oxford*
  • Dr Chris Ives, University of Nottingham*
  • Professor John O’Neill, Political Economy Institute, University of Manchester*
  • Dr Ian Mell, Manchester Urban Institute, University of Manchester
  • Professor Jim Harris, University of Cranfield*
  • Dr Elia Apostolopoulou, University of Cambridge Conservation Research Institute*
  • Dr Louise Carver, Lancaster University Environment Centre
  • Professor Sian Sullivan,  Research Centre for Environmental Humanities, Bath Spa University
  • Dr Helen Phillips, German Centre for Integrative Biodiversity Research (iDiv)
  • Professor James Bullock, Centre for Ecology and Hydrology
  • Dr Rupert Read, University of East Anglia
  • Dr Joseph Franklin, AECOM
  • Charles Russ, AECOM
  • Tom Butterworth, WSP UK
  • Rosemary Waugh, Thames Water*
  • Rebecca Elliott, Thames Water*
  • Andrew Whitaker, Home Builders Federation
  • James Harris, RTPI
  • Tom Kerry, RTPI
  • Dr Nick White, Natural England 
  • Clare Warburton, Natural England
  • Max Heaver, Defra*
  • Lindsay Roome, Defra
  • Emma Luke, Defra*
  • Andrew Ruck, Defra*
  • Lauren Moore, Defra*

* denotes stakeholders who acted as external reviewers of the POSTnote.

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