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A whistle-stop tour of the Biodiversity Net Gain (BNG) on new developments

25 June 2021

In this article, Andrew Batterton and Charlotte Marshall review the Who, What, Why, When and How of Biodiversity Net Gain (BNG) on new developments including what this means for the future.

Who and What 

Although BNG is not a new concept, the government had decided that new developments must measurably increase biodiversity, either as part of the development or within the local area. The Environment Bill 2020 (if passed) will introduce mandatory BNG provisions as part of planning permission application submissions to local authorities. 


Identifying the underpinning rationale is simple "flourishing ecosystems mean cleaner air and water, and well-tended green spaces… contribute significantly to mitigating climate change"  (Department for Environment, Food & Rural Affairs and Villiers 2019). 

In an era where more focus is being given to the human impact on the earth, legislative changes structured around environmental protection are hardly surprising. The Environment Bill is a significant piece of legislation and BNG targets are only one (small) element.


The 'how' is arguably the most important aspect of understanding the future of BNG. 

The Bill will amend the Town and Country Planning Act 1990 (TCPA) and will require planning applications to evidence (save for some exceptions) a 10% increase in BNG either on site or in the local area. In a future article we will consider these exceptions and the delivery of BNG off site. 

BNG will be measured in practice through obtaining pre and post development ecological appraisals. Gain Plans (also referred to as Net Gain Plans) produced by ecological experts will be required when submitting applications. These will then either become pre-determinations to, or conditions within, planning consents.

So how will BNG be measured under an ecological appraisal? The primary tool is the DEFRA Biodiversity Metric 2.0 (We note that there has recently been a government consultation into Biodiversity Metric 3.0 which was due to launch Spring 2021, however, it has still not been finalised.) This tool allocates 'biodiversity units' for the size and quality of 'habitats', the latter is measured on 4 key elements, which are each scored: 

  1. Distinctiveness- the value of any given habitat the local wildlife
  2. Condition- the quality of the habitat with reference to set criteria
  3. Strategic Significance – whether the habitat is locally significant
  4. Connectivity – the proximity of the habitat patch to similar or related habitats

The scores of pre and post development ecological appraisals will then be compared to calculate the variation in biodiversity. There is also a possible option to “purchase” biodiversity units from DEFRA. 


The Bill is yet to pass into law and the timetabling for it has been delayed by Covid-19. As a result, it is unlikely to receive royal assent until Autumn 2021 (at the earliest). 

With the new rules unlikely to be mandatory for a further 2 years after this (during the transition period), implementation will likely vary with each local authority taking a slightly different approach to this new mandate. 


BNG is already a material consideration in the determination of planning applications for new development for which there is a strong policy objective in national planning policy.  The prospect of the Bill coming into force will put this on a statutory footing and mandate at least a 10% improvement over the status quo.  Unless exceptions apply, this will provide real challenges for urban development which we predict will lead to a cottage industry of off-site credit-based mitigation schemes.  Whilst there are likely to be opportunities for the private sector to secure compensatory mitigation land, we anticipate that local authorities and other public bodies (with land assembly powers) will need to ensure that implications for the delivery of its local plan have been taken into account and suitable land identified and safeguarded.  BNG will clearly be an early consideration for developers as part of development appraisals and they will want to work closely with local authorities to understand its expectations in the pursuit of support for their proposals. 

Look out for Part 2 of this article, where we consider the exceptions to the mandatory 10% BNGs under the Bill and how in practice BNG might be delivered offsite utilising the "purchase” of biodiversity units from DEFRA. 

Authors: Andrew Batterton and Charlotte Marshall

If you are considering how the issues in this article may affect you, please contact a member of our UK public sector team to discuss how we might assist you.

Further Reading