Decoding Biodiversity Net Gain Tom Docker 12 February 2024

Decoding Biodiversity Net Gain

Mandatory Biodiversity Net Gain, commonly referred to as BNG, emerged as one of the flagship announcements in the government’s most significant overhaul of environmental legislation in a generation: the Environment Act 2021.

As we step into the realm of BNG, Tom Docker, managing director at Middlemarch, takes you on a journey beyond the legislative jargon, unravelling the layers of BNG’s complexity. He explores not only what BNG is but, more importantly, what it means for you and how Middlemarch can help navigate a rapidly changing legislative and policy landscape.


As a concept, BNG is very simple, requiring development or land management activities to leave biodiversity in a measurably better state than it was prior to any intervention. As ever, the reality of BNG is far more complex and nuanced, creating as many questions as it provides answers. The first such question, and a good starting point is… What do we mean by biodiversity, and how can meaningful net gain be delivered?

The term biodiversity describes to the richness and variability of the flora and fauna that make up our natural world. In the context of BNG, however, this definition has a much narrower focus, referring to the value and condition of habitats within the area of study. A longstanding criticism of ecological protections in the UK has been a perceived focus on species protection over true landscape-scale conservation. Therefore, the shift towards a greater focus on habitats is welcome; however, in order for BNG to achieve a true net gain, complete with benefits to species known to be in decline, it is essential to target the right habitat, in the right location, with the right long-term management. Only when all three criteria are met can BNG unlock its true potential and make a transformative difference to the alarming declines witnessed in recent decades.


BNG has been portrayed as a constraint to development in some circles; however, many forward-thinking developers have come to view BNG as an opportunity to demonstrate their sustainable credentials and, with good design, save money. The most common misconception about BNG is that it automatically necessitates a loss of developable area, making projects less economically viable. By taking biodiversity into account from the outset of a project (i.e., during site selection, before the architect’s pen has touched the paper) and gaining a thorough understanding of both constraints and opportunities, it is possible to optimise the design from both a development and biodiversity perspective, significantly reducing the time and cost associated with retrofitting ecology into a pre-designed masterplan.


A further misconception is that BNG should always be delivered on-site. It is helpful to take a nuanced view that balances the cost of delivery (including the opportunity cost associated with reducing development area) with the true net gain that can be achieved. It is important to deliver net gain as close as possible to the source of any loss; however, striving to achieve net gain on site will not always deliver the best outcome for biodiversity (right habitat, right place, right management). BNG will often be achievable on site if sustainable design has been a consideration from the outset. However, the optimal solution will often involve a combination of good-quality on-site habitat retention and landscaping (in accordance with the mitigation hierarchy), along with well-designed offsetting that provides a contribution to landscape-scale green infrastructure targets.


With a UK-wide cohort of BNG experts and an industry-leading nature-based solutions team, our in-house experts bring a diverse range of experience and can provide specialist knowledge in biodiversity and other environmental metrics. We can support you in creating and implementing a strategy for BNG to meet or exceed mandatory requirements, spanning baseline assessments and metric calculations to high-quality habitat design and creation that complements your project and supports local and national nature recovery targets.