The top three are 'live links' you can Download the principles and the guidance by clicking on them:
• Biodiversity Net Gain – Good practice principles for development (2016)
• Biodiversity Net Gain – A practical guide (2019)
• Biodiversity Net Gain – Case studies (2019) – also available individually on the
Resource Hub 

If you wish to read sources, feel free to cut and paste the following website addresses into your browser

Latest academic research - 

Exploring the ecological outcomes of mandatory biodiversity net gain using evidence from early-adopter jurisdictions in England  The Society for Conservation Biology (wiley.com)

Other Sources

British Ecological Society. 2020. Mandatory Biodiversity Net Gain may not deliver the
desired outcomes for nature. [Online]. Available from:
https://www.britishecologicalsociety.org/

Cornwall Council. 2020. Biodiversity Net Gain. [Online]. Available from:
https://www.cornwall.gov.uk/environment-and-planning/

Cornwall.gov.uk. 2021. Biodiversity Net Gain – Cornwall Council. [online] Available
at: https://www.cornwall.gov.uk/environment-and-planning/ 

Department for Environment, Food & Rural Affairs. 2019. Net gain: Summary of
responses and government response. [Online]. Available from:
https://www.gov.uk/government/

Department for Environment, Food & Rural Affairs. 2020. Policy paper 30 January
2020: Environment Bill 2020 policy statement. [Online]. Available from:
https://www.gov.uk/government/publications/environment-bill-2020/

Department for Environment, Food & Rural Affairs, The Rt Hon Theresa Villiers MP.
2019. Government introduces ground-breaking Environment Bill. [Online]. Available
from: https://www.gov.uk/government/

Dunn, L. 2019. Biodiversity Net Gain – what are the key features? [Online]. Available
from: https://www.localgovernmentlawyer.co.uk/planning

Easton, J., Bell, C. 2020. The no-nonsense guide to biodiversity net gain. [Online].
Available from: https://localgovernmentlawyer.co.uk/

Environment Analyst. 2019. Defra firms up Net Gain requirements. [Online].
Available from: https://environment-analyst.com/

Forest Research. N.D. Biodiversity. [Online]. Available from:
https://www.forestresearch.gov.uk/tools-and-resources/

Homes England. 2018. Homes England strategic plan 2018 to 2023. [Online].
Available from: https://www.gov.uk/government/publications/homes-englandstrategic-plan-201819-to-202223

Lodders. 2020. Biodiversity net gain – FAQs. [Online]. Available from:
https://www.lodders.co.uk/blog/building-with-nature-planning-seminar-faqs/

McClean, K. 2020. Biodiversity net gain: Barrier or opportunity? [Online]. Available
from: https://www.theplanner.co.uk/opinion/

Ministry of Housing, Communities, & Local Government. 2019. National Planning
Policy Framework. [Online]. Available from: https://assets.publishing.service.gov.uk/

Ministry of Housing, Communities, & Local Government. 2019. Natural Environment.
[Online]. Available from: https://www.gov.uk/guidance/natural-environment

National Biodiversity Network. 2019. State of Nature 2019. [Online]. Available from:
https://nbn.org.uk/stateofnature2019/reports/

Natural England. 2019. The Biodiversity Metric 2.0. [Online]. Available from:
http://nepubprod.appspot.com/publication/5850908674228224

Thompson, A. 2020. The Environment Bill and biodiversity net gain. [Online].
Available from: https://www.pbctoday.co.uk/news/planning-construction-news/

UK Parliament. Environment Bill 2019-2021. [Online]. Available from:
https://services.parliament.uk/bills/2019-21/environment.html 

Wood, N. 2020. Explaining Biodiversity Net Gain. [Online]. Available from:
https://www.todaysconveyancer.co.uk/