Biodiversity Net Gain: Future developments must improve wildlife habitats

The UK Government has announced new English developments will be required to demonstrate a 10% increase in biodiversity on or near development sites

The Chancellors’ 2019 spring statement indicated it will be mandatory for all development in England to deliver a ‘Biodiversity Net Gain’. A more recent government statement (23 July 2019) outlines further details about how the Biodiversity Net Gain requirement will be defined, as well as exemptions, protections for ‘irreplaceable habitats’, and how net gain will be administered. The Government proposes that the requirement will come in force after a two-year ‘transition period’ after the new Environment Bill for England receives royal ascent.

A number of the partner organisations in the Partnership for Biodiversity in Planning are engaged in the further discussions about implementing the Biodiversity Net Gain requirement. In addition, CIEEM, IEMA and CIRIA, with support from Balfour Beatty, are currently revising their good practice guidance on Biodiversity Net Gain. This article touches on some of the key issues raised and still to be resolved.

Measuring Biodiversity gains

Natterer’s Bat (Credit: Daniel Hargreaves)

The summer statement goes a little further in clarifying how DEFRA will define ‘Net Gain’ to biodiversity, establishing the principle that planning permission should only be given if a new development project increases rather than reduces levels of biodiversity present on a site. Evidence of an increase in biodiversity will require a baseline assessment of what is currently present on a site and then an estimation how proposed designs will add to that level, and latterly supported by post-construction evidence that a 10% gain has been delivered.

Measurement of pre and post-construction biodiversity levels will be based on DEFRA’s Biodiversity Metric 2.0‘. DEFRA has proposed to use four components, each with specific ‘metrics’ or indicators, to create an indicative score for biodiversity quality on the site (and offsite where applied) pre and post-construction:

  • Distinctiveness: the score is assigned based on DEFRA’s habitat classification (8 = very high to 0 = very low distinctiveness)
  • Condition: the score is based on DEFRA criteria associated to different habitats (e.g. cropland, grassland, heathland, lakes, woodland, urban, wetlands)  (3 = good to 1 = poor condition)
  • Strategic significance: the score is based on landscape-scale factors defined nationally and locally (1.15 = high to 1 = low significance)
  • Habitat connectivity: the score is based on ‘habitat aggregation’ calculation (1.15 = high to 1 = low connectivity)

This is then used to calculate the onsite (and offsite) baseline score:

Baseline biodiversity units = Distinctiveness x Condition x Significance x Connectivity x Area in hectares (or length in km)

A biodiversity score is calculated based on credits assigned to each of these components and then multiplied by the area or length (if it is a linear corridor) of the site. The predicted gain is then calculated in the same way, adding-in new biodiversity elements and new components relating to risks associated to the development, regarding:

  • Spatial risk: distance of offset from site
  • Temporal risk: time for habitats to reach target condition
  • Delivery risk: difficulty of habitat creation

These elements are applied to calculate the onsite (and offsite) post-development score:

Post-development biodiversity units = Distinctiveness x Condition x Significance x Connectivity x Area in hectares (or length in km) / Spatial x Temporal x Delivery risks

The Biodiversity Net Gain is then a fairly simple calculation:

Biodiversity units created = Post development biodiversity units – Baseline biodiversity units

DEFRA emphasizes that the proposed Biodiversity Net Gain 2:0 metric is just one part of the biodiversity puzzle. Existing legislation protecting key species, habitats and designated sites remain. The metric also does not include species composition, habitat structure, ecological functionality or people’s use or values associated to biodiversity. These all need to be assessed to gain a full picture of the biodiversity contribution in a site.

Exemptions from Net Gain requirement

DEFRA’s initial consultation document outlined their aim of creating a more ‘level playing field’ for developers, through a standardised requirement regarding biodiversity. The government response tempers this ambition somewhat introducing various exemptions for specific development types, including:

  • major infrastructure projects and marine sites
  • certain urban brownfield sites, if they don’t contain protected or priority habitats (e.g. open mosaic habitat) or ‘face genuine viability difficulties’
  • smaller ‘minor’ development sites (fewer than 10 residential units or an area of less than 0.5 hectares) will be offered a more simplified requirement and potentially lower than 10% gain
  • building extension projects

Compensation for biodiversity loss

The interpretation of Biodiversity Net Gain has been further tempered, as it includes the option for off-site’ compensation’ as an option of last resort or purchasing of biodiversity credits, if biodiversity losses are unavoidable in accordance with DEFRA’s mitigation hierarchy. Some conservation groups remain concerned that the concept of compensation might actually enable developments that would not have been permitted otherwise, as it opens the way to developers to opt for investments to off-site wildlife areas rather than adding to the site in question.

DEFRA’s Biodiversity Mitigation Hierarchy

Certain ‘irreplaceable habitats’ will not be reflected by this mitigation  approach and will be protected however, including: ancient woodland, ancient and veteran trees, blanket bog, limestone pavement, sand dunes, salt marsh and lowland fen in accordance with the National Planning Policy Framework (p.68-9, 2019) and the Conservation of Habitats and Species Regulations (2017).

Local decision makers will need to agree biodiversity net gain plans with the developers, as well as specify by a condition, planning obligation or conservation covenant, how long the developer should maintain the habitat enhancement, with a minimum requirement of 30 years. If offsite compensation is agreed, as a last resort, in that plan, local authorities will review developers’ plans to ensure they deliver compensation through local habitat creation projects. If suitable local projects are unavailable, the government indicates nationally strategic habitats can be invested in.

Administration, monitoring and management

The government response has given Natural England responsibility for rolling out the Biodiversity Net Gain requirement. It calls for the creation of Local Nature Recovery Strategies to map out current biodiversity levels and identify opportunities for enhancement. These recovery strategies are likely to be produced by Local Nature Partnerships and should work hand-in-hand with Local Environment Record Centres who retain historical and current biodiversity data. This means that any developers who might consider illegal clearing of a site of biodiversity before seeking planning permission will be subject to evidence of the biodiversity known to exist onsite before the developer engaged with it, and would face the consequent penalties of such activities.

Developers will be expected to deliver habitat creation or enhancement as part of delivering mandatory biodiversity net gain, to be maintained for at least 30 years, with local planning authorities allowed to require longer term protection as a planning condition, obligation or conservation covenant. The new Environment Bill will legislates for Conservation Covenants which are private, voluntary agreements between a landowner and a “responsible body”, such as a conservation charity or government body. The covenant binds the initial landowner and subsequent landowners to ensure long-term conservation and environmental benefits on net gain sites.

Further details about the new mandatory Biodiversity Net Gain requirement are outlined in the government’s response to the consultation. There was a consultation on the Net Gain Metric 2.0 until 29 February 2020.


Partner responses:

  • The Bat Conservation Trust response to the consultation is available here.
  • The UK Green Building Council response is available here.
  • The RTPI response is available here.
  • The Wildlife Trust response is available here.



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