A Developer’s Guide to Biodiversity Net Gain


In the face of a half-century-long decline in biodiversity, the Environment Act 2021 has ushered in a pivotal change: a legal requirement for certain developments to achieve a 10% Biodiversity Net Gain (BNG). This measure aims to ensure that new developments not only mitigate harm to our ecosystems but actively improve them, signalling a new era of ecological responsibility for developers.

Evaluating Biodiversity Net Gain

The process of assessing BNG begins with a thorough ecological survey, going beyond the traditional scope to paint a complete picture of the site’s biological tapestry. Specialists conduct these evaluations, equipped with advanced methods and metrics to ascertain whether a development will detract from, maintain, or enhance biodiversity. This analysis, rooted in sophisticated ecological models and data, must be meticulously planned to align with the long-term viability of the development and the sustainability of the local ecosystem.

Understanding Environmental Assessments

Developers must navigate several types of environmental assessments:

  1. Environmental Impact Assessment (EIA): A comprehensive analysis that assesses the potential social, ecological, economic, and health impacts of a project. It is particularly crucial for developments likely to have significant environmental effects, such as large-scale urban projects or industrial developments.
  2. Ecological Impact Assessment (EcIA): This assessment zooms in on the ecological consequences of a project, scrutinizing potential changes to habitats and species and outlining strategies to avoid, offset, or mitigate negative impacts.
  3. Preliminary Ecological Appraisal (PEA): Often the first step in the assessment process, the PEA is a swift evaluation that identifies ecological constraints and potential enhancements to the site’s natural environment.

When Is an Ecological Survey Necessary?

A detailed ecological survey is imperative when a development might impact habitats known to harbor European Protected Species (EPS). The presence of features such as traditional buildings, large gardens, water bodies, heathlands, and woodlands, among others, could trigger the need for comprehensive ecological assessments to ensure compliance with environmental regulations.

Implementing Biodiversity Net Gain

To achieve BNG, pre- and post-development biodiversity conditions are meticulously compared. The data collected is transformed into ‘biodiversity units’ using metrics such as the updated Natural England Metric 3.0. The BNG, often expressed as a percentage, is determined by the variation in these units, accounting for both onsite enhancements and potential offsite compensation.

The New Environment Bill and Its Implications

The upcoming Environment Bill mandates BNG for most new developments, enshrining the 10% net gain requirement into law. All planning permissions will hinge on the approval of a robust biodiversity plan, ensuring that developers are not only planning responsibly but also contributing to the broader ecological network.


The movement towards mandatory BNG is a reflection of an evolving environmental ethos. Developers are called upon to integrate these considerations into their planning, transcending mere compliance to champion environmental enhancement. Mastery of EIAs, EcIAs, PEAs, and BNG assessments is essential for the successful delivery of development projects that are both economically viable and ecologically enriching.

Our Expertise

With extensive experience in BNG calculations and a deep understanding of various metrics, our team is well-versed in delivering assessments that meet both regulatory standards and the developer’s need for practicality. We utilize data from Preliminary Ecological Assessments to streamline the BNG process, ensuring accuracy while minimizing costs and time expenditures.

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author avatar
Humperdinck Jackman
Leads the daily operations at ESG PRO, he specialises in matters of corporate governance. Humperdinck hails from Bermuda, has twice sailed the Atlantic solo, and recently devoted a few years to fighting poachers in Kenya. Writing about business matters, he’s a published author, and his articles have been published in The Times, The Telegraph and various business journals.


Matt Whiteman

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