Biodiversity Net Gain Explained: What BNG Actually Means in 2026

Biodiversity Net Gain (BNG) is the single biggest change to UK planning since the introduction of the NPPF. Since February 2024 (and April 2024 for small sites), almost every new development in England has to leave biodiversity measurably better off than it found it — by at least 10%, for at least 30 years. This guide explains what that means in practice, without the jargon.

What is Biodiversity Net Gain?

BNG is a legal requirement under the Environment Act 2021. A development can only get planning permission in England if it can demonstrate, using a government-approved spreadsheet (the statutory biodiversity metric), that the habitats on site after the build are worth at least 10% more 'biodiversity units' than the habitats that were there before — and that those gains are secured and maintained for 30 years.

It applies to development consented under the Town and Country Planning Act, including small sites, with a separate (and slower) regime coming for Nationally Significant Infrastructure Projects.

How the 10% is actually measured

Three habitat types are scored separately and each must be 'net gain' or better: area habitats (grassland, woodland, scrub), hedgerow habitats, and watercourse habitats. The statutory metric multiplies habitat area by distinctiveness, condition, strategic significance and a time-to-target factor, and applies risk discounts the further off-site you go.

That last point matters. Replacing ancient woodland on the other side of the country with a newly planted plantation does not balance the maths — the metric is deliberately punitive towards low-distinctiveness, off-site, slow-to-mature habitats.

The three-step hierarchy

Defra's BNG policy follows a strict order. You can only move down the list if the step above is genuinely impossible:

• 1. On-site gain — create or enhance habitat within the red line of the development.
• 2. Off-site gain — buy or create biodiversity units on another piece of land (typically through a habitat bank registered on the BNG register).
• 3. Statutory biodiversity credits — buy credits from Defra as a last resort. They are deliberately expensive, to discourage skipping steps 1 and 2.

BNG exemptions (the bit everyone asks about)

Not every development needs to deliver 10% gain. The main statutory exemptions in 2026 are:

• Householder applications (extensions, outbuildings within the curtilage of a home).
• Self-build and custom-build of up to 9 dwellings on a site under 0.5 hectares.
• Developments that impact less than 25 sq m of on-site habitat and zero linear metres of hedgerow.
• Urgent Crown development, high-speed rail, and certain biodiversity gain sites themselves.

The Biodiversity Gain Plan

If your scheme is in scope, you'll need to submit a Biodiversity Gain Plan as a condition of planning. The plan sets out the pre- and post-development metric scores, how the 10% gain will be delivered, who will manage the habitat, and how it will be monitored and secured for 30 years (usually via a section 106 agreement or a conservation covenant with a responsible body).

The plan has to be approved by the LPA before development can lawfully commence — not before permission is granted. That's a common misunderstanding that costs developers months.

Who actually does BNG work?

On the developer side: project managers, planning consultants and landscape architects sit alongside ecologists. On the technical side, the BNG metric assessment must be carried out by a 'competent person' — in practice, a Senior or Principal Ecologist with CIEEM membership and demonstrable BNG training.

This is why the BNG-competent senior ecology market is the tightest it has been in a decade. The pipeline of people qualified to sign off the metric has not kept up with mandatory demand.

What BNG means if you're a candidate

If you're an ecologist with 3+ years' experience and you can confidently run the statutory metric, you are in the strongest negotiating position the profession has ever offered. Get BNG training, get on a couple of live schemes, and your next move is worth £8–12k more than it was 18 months ago.

What BNG means if you're an employer

Build your pipeline now. The Senior–Principal layer is moving fastest in the market. Compressed two-stage interview processes, hybrid working and funded BNG CPD are the offers winning the people you want. Talk to us about your BNG hiring plan and we'll benchmark your offer against the live market for free.