Biodiversity Net Gain

Biodiversity Net Gain and the Council of the Isles of Scilly

The 12th February 2024 marked the national adoption of Biodiversity Net Gain (BNG), following the enactment of the Environment Act (2021) and its two year transition phase. For more information on this and what is expected by Central Goverment, please visit the website: Biodiversity net gain - GOV.UK (

What happens now?

For development in the Isles of Scilly, all new major developments will need to deliver at least 10% net gain for nature. We will expect a completed Biodiversity Net Gain metric to be submitted with every major planning application. How the Net Gain will be delivered will need to be set out in a Biodiversity Gain Plan. The submission of these documents will be a validation requirement. The BNG metric needs to be submitted as an Excel file, and the BNG plan as a PDF.

The metric will need to show a minimum 10% gain for habitats, hedges, and rivers (if applicable to the development site) and the Biodiversity Gain Plan will need to set out how this will be delivered over the 30 year post development period.

Who completes the Biodiversity Net Gain metric and writes the Biodiversity Gain Plan?

A competent and suitably qualified ecologist needs to complete the BNG metric and produce the BNG Gain Plan. This is because the BNG metric needs the UK Habitat Classification methodology to be used for the on site field survey, and this requires a good level of habitat survey skills. If any watercourses are present within the site a Modular River Physical survey (MoRPh) will be required in order to complete the rivers tab of the BNG metric.  

What if we can’t manage the 10% minimum net gain units on site?

If a development cannot achieve an on site net gain in each of the applicable areas (i.e. all of habitats, hedges and rivers, if they are on site) offsetting is possible. This is the purchase of units from another provider, which may be available from a range of suppliers such as local authorities, businesses or charities.

Does the Council of the Isles of Scilly have off-site units available to buy?

The Council of the Isles of Scilly does not currently have units to offer. However we are working with key local landowners and managers to create a BNG offset unit offer and will update this note as that develops. In the meantime developers may wish to investigate one to one agreements with local landowners, or the national BNG credit scheme available through DEFRA. The Council of the Isles of Scilly are also working with Cornwall Council through the Nature Recovery Strategy Network to investigate whether BNG units which are available in Cornwall on the mainland may be used to offset impacts on the islands.

What is the advantage?

Biodiversity net gain aims to build resilient networks for nature with space for nature within development sites. Such spaces are also valuable for people using the site, and common development features such as SuDS ponds, parks, perimeter hedges and footpaths all count towards your net gain on site. For sites which achieve break even on site but which cannot achieve the 10% minimum off-site BNG allows the collection of funds from developers through the offsetting route to feed into building strategic nature recovery networks.

What is happening next?

The next piece of Biodiversity Net Gain is the introduction of the Small Sites Metric on the 2nd April 2024. At this point minor applications (this includes single new dwellings but excludes householder applications for things like extensions, loft conversions etc) will need to complete the Small Sites Metric and submit this with their planning application. The Small Sites Metric is a simplified version of the metric used for major applications. Both metrics are issued by DEFRA.