Biodiversity Net Gain: England’s 10% nature mandate

What Biodiversity Net Gain requires

Biodiversity Net Gain is a planning requirement in England, introduced by the Environment Act 2021.

Schedule 14 of the Act sets a biodiversity gain objective: the biodiversity value attributable to a development must exceed the pre-development value of the on-site habitat by at least 10%^[1].

In other words, every covered development must leave nature measurably better off than it found it — not merely avoid harm. That gain is not assessed by judgement; it is calculated with a government metric and locked in through the planning system^[3].

The phased commencement

BNG did not switch on all at once. It was phased by development type to give the market time to build the surveying, metric and habitat-banking capacity the rule depends on^[5].

BNG applies to England, and it sits alongside — rather than replacing — existing habitat and species protections^[3].

Some development is exempt. The de minimis exemption removes development that does not affect priority habitat and impacts less than 25 square metres of non-priority habitat, or less than 5 metres of linear habitat such as hedgerows^[5].

Householder applications and self-build or custom housebuilding are also exempt, as are applications made before the commencement dates^[5].

The biodiversity metric

The unit of account for BNG is the statutory biodiversity metric. It converts habitats into “biodiversity units”, a proxy for biodiversity value, using habitat type, size, distinctiveness, condition and location in the local area^[3].

The calculation runs twice: once for the baseline habitat before development, and once for the proposed habitat afterwards. The difference is the gain or loss, and the post-development value must exceed the baseline by at least 10%^[3].

A completed metric tool must be submitted as part of a Biodiversity Gain Plan, which the local planning authority must approve before development can begin^[3].

Small developments can use the same statutory metric or a simpler small sites metric, which fixes habitat condition values and removes the need for a full condition assessment^[4].

The mitigation and gain hierarchy

BNG reinforces the long-standing mitigation hierarchy — avoid harm first, then minimise it, then compensate for what remains — and layers a gain hierarchy on top for how the 10% is delivered^[2].

Developers must work through the gain hierarchy in order, combining options only after exhausting the higher ones^[2].

Statutory biodiversity credits are deliberately positioned as a last resort and are intended to be more expensive than securing units locally, so that the credit route does not undercut real habitat creation^[2].

Thirty years of management and monitoring

A gain on paper is not enough. For off-site gains and significant on-site gains, the habitat created or enhanced must be secured, managed and maintained for a minimum of 30 years^[2].

Those obligations are set out in a legal agreement — typically a planning obligation or a conservation covenant — and the habitat must reach the distinctiveness and condition the metric assumed^[2].

This long horizon is what has created the habitat-banking market: operators that create and manage habitat sites in advance, register the units on Natural England’s biodiversity gain sites register, and sell them to developers who cannot deliver enough gain on their own land^[3].

BNG, TNFD and the UK SRS direction

BNG is a site-level planning obligation, not a corporate reporting standard.

But it is fast becoming a source of the auditable, quantified nature data that corporate disclosure frameworks have lacked.

The Taskforce on Nature-related Financial Disclosures published its recommendations in September 2023, structured around the same four pillars — governance, strategy, risk and impact management, and metrics and targets — that run through the climate frameworks^[6].

For a developer or landowner, BNG delivery generates exactly the kind of evidence TNFD-aligned reporting asks for: measured habitat baselines, secured gains, and long-term management commitments.

The current UK Sustainability Reporting Standards focus on general and climate disclosure, but the IFRS Foundation’s consolidation of TCFD and its work alongside TNFD point clearly towards nature following climate into the mandatory perimeter over time.

For where biodiversity sits in the wider UK picture today, see our biodiversity reporting and ESG reporting requirements analysis.

Biodiversity Net Gain: frequently asked questions