Biodiversity Net Gain

Chapter 1: How We Got Here I f you are reading this book, you are probably annoyed. You have been told that your next development, the one you have been working on for months, the one with the planning drawings already submitted or about to be submitted, now needs something called Biodiversity Net Gain. Your planning consultant mentioned it. Your architect flagged it. Your land agent said something about it when you were negotiating the site purchase. And now you are sitting here trying to understand what it is, what it costs, and whether it is going to kill your scheme. I understand the frustration. I have watched this regulation land on the construction industry like a rock through a greenhouse roof. One day it was a rumour. The next day it was law. And the guidance, when it finally arrived, was written by ecologists for ecologists in a language that might as well have been Elvish. So let us start at the beginning. Why does this exist? The short answer is that Britain has destroyed a very large proportion of its natural environment, and the government decided that the planning system should help fix it. The longer answer requires a small amount of context. The United Kingdom has lost more of its natural biodiversity than almost any other country in western Europe. The Natural History Museum reported in 2020 that Britain ranked last among the G7 nations for the proportion of natural biodiversity remaining. We have lost 97 per cent of our wildflower meadows since the 1930s. We have lost half our hedgerows since the Second World War. We have lost about half our native woodland. Our rivers are in a documented ecological crisis. This did not happen because developers are bad people. It happened because for decades, the planning system treated ecological impact as a box-ticking exercise. An ecological survey would be commissioned, it would note the presence or absence of protected species, mitigation would be proposed (move the newts, relocate the bats), and the development would proceed. The overall direction of travel was always the same: habitats were destroyed and never replaced. Mitigation meant “do the minimum to avoid breaking the law.” Enhancement meant nothing, because nobody was measuring it. The political response to this has been building for years. The National Planning Policy Framework introduced the concept of “net gains for biodiversity” as early as 2012, but it was Biodiversity Net Gain 12 aspirational rather than mandatory. Councils could ask for it. Developers could ignore the request. Most did. The step change came with the Environment Act 2021, which received Royal Assent on 9 November 2021. Among many other things, the Act amended the Town and Country Planning Act 1990 to insert a mandatory requirement for Biodiversity Net Gain on all qualifying developments in England. After a period of preparation and consultation, the requirement became live in stages: 12 February 2024: BNG mandatory for all major developments (10 or more dwellings, or sites of 1 hectare or more). 2 April 2024: BNG mandatory for small sites (fewer than 10 dwellings on sites under 1 hectare). 6 August 2026: Significant amendments came into force under SI 2026/790, including the new 0.2-hectare exemption, the removal of the self-build exemption, and the relaxation of the biodiversity gain hierarchy for minor development. 2 November 2026: BNG mandatory for Nationally Significant Infrastructure Projects (NSIPs), including power stations, major highways, railways, reservoirs, and large-scale commercial developments. This date was originally expected to be May 2026 but was pushed back due to the scale and complexity of NSIP schemes. As of the date this second edition is published, BNG has been mandatory for over two and a half years. Every qualifying