Biodiversity Impact Assessment

Biodiversity Impact Assessment Calculator

Thames Valley Environmental Records Centre has developed a locally derived version of the DEFRA biodiversity offsetting metric for Berkshire and Oxfordshire.  This is based on our knowledge of the habitats that TVERC has mapped across the two counties.  It also reflects local conservation priorities as set out by Local Nature Partnerships and local authority biodiversity action plans.

As an unfunded project, development of TVERC’s Biodiversity Impact Assessment Calculator proceeds as and when funds are available to TVERC.  TVERC welcomes feedback from all of the users of the BIAC.  This feedback will be collated and reviewed annually in January and any updates or changes will be made according to the funding that TVERC has available from its own funds at that time.  A new version will be release annually in March each year, with release notes to indicate what changes have been made. 

TVERC cannot guarantee that all issues raised in one calendar year will be resolved, due to limited funding.  If a customer wishes specific changes to be made outside of this process, these can be funded via a separate project and any changes that result will be released to all partners and on the TVERC website once the change has been implemented.

The BIAC comes with release notes detailing the changes made for the current version, a guide to using the BIAC, a literature review of time to target condition and a comparison of different calculators.

The Biodiversity Impact Assessment Calculator is available to download here Version 2.1.1 was made possible by funding from Oxfordshire County Council.

If you have any feedback on the TVERC BIAC, please contact TVERC on

Biodiversity Impact Assessment for Net Gains

TVERC are offering a biodiversity impact assessment service for biodiversity net gains to developers and ecological consultants for development sites.  We will provide you with an impartial assessment of the development plans and their impact and indicate whether or not the current plans deliver net gains for biodiversity.  We will also tell you whether the on-site habitat creation or restoration proposals are appropriate for the Thames Valley region.


There is strong policy support for securing measurable net gains for biodiversity as a result of development.

Paragraph 170 of the revised National Planning Policy Framework (NPPF) says that ‘Planning policies and decisions should contribute to and enhance the natural and local environment by…

d) minimising impacts on and providing net gains for biodiversity…’.

Paragraph 174 says that ‘To protect and enhance biodiversity and geodiversity, plans should:…

b)…identify and pursue opportunities for securing measurable net gains for biodiversity…’.

In addition, a number of Local Plans in Berkshire and Oxfordshire now include policies that require developments to deliver net gains for biodiversity.

Best Practice Guidance

CIEEM, together with CIRIA and IEMA have published Principles and Guidance for Biodiversity Net Gain on the CIEEM website.

How It Works

TVERC will use its own habitat data and information provided by you on the current site condition and development proposals to calculate the number of biodiversity units on the existing site and the number that will be provided by the proposed site.  We will provide you with a short report and a copy of the calculator and tell you whether the proposals deliver net gains for biodiversity or not.  We will also provide advice on the appropriateness of the proposed on-site habitat management or restoration proposals using our extensive knowledge of the habitats and landscapes of Berkshire and Oxfordshire.

You will need to supply TVERC with the following:

  • A plan of the existing site including habitat boundaries, as an image file, GIS data or CAD file (preferred formats are ESRI .shp or .dxf CAD files);
  • A copy of the phase 1 survey report for the site;
  • A plan of the proposed site layout with habitat boundaries, as an image file, GIS data (ESRI .shp) or CAD(.dxf) file;
  • Copies of any habitat or landscape management plans for the proposed site.


The charge for this service is £275 + VAT

Response Time

  • We will usually process a request within 24 hours and send you a quote which needs to be signed and returned, after which we usually complete searches within 10 working days.
  • Searches required within 1-3 working days will receive a 100% surcharge.
  • Searches required within 4-6 days will receive a 50% surcharge
To request the Biodiversity Net Gain service, please complete this form.

For more information, or to discuss your requirements please contact TVERC on 01865 815451 or