What Is Biodiversity Net Gain (BNG) and Why Does It Matter?

A developer in Staffordshire submits a scheme to planning, then hits a wall: their application will not be validated until one condition is met. That condition is biodiversity net gain. It is not optional, and their application can’t move forward until this has been resolved.

Biodiversity Net Gain (BNG) is a legal requirement for development in England to leave nature in a measurably better state than it was before building started. Every qualifying project has to deliver at least a 10% increase in biodiversity value, measured in biodiversity units, and that gain has to be maintained for at least 30 years.

That one rule has changed how sites are designed, how land is valued, and how farmers think about their least productive fields. Here is what it means, how it works, and why it matters, for the developers who have to deliver it and the landowners who can earn from it.

What is biodiversity net gain?

Biodiversity net gain is an approach to development and land management that ensures a project leaves habitats in a better state than it found them. Rather than simply limiting the damage, the developer has to hand nature back more than was lost.

It became mandatory in England under the Environment Act 2021, through Schedule 7A of the Town and Country Planning Act 1990.

The requirement applied to major developments from 12 February 2024 and to small sites from 2 April 2024, and it extends to nationally significant infrastructure projects from November 2026. For most planning applications now, demonstrating BNG is a condition of permission.

So what is BNG in practice?

It is a measurable promise, written into the planning system and enforced through legal agreements. A council cannot wave a scheme through on good intentions. The gain has to be calculated, secured, and monitored. When people ask for the short version, the BNG meaning is simply that: build, but leave more nature behind than you take.

The 10% biodiversity net gain rule

If a site holds 50 biodiversity units before development, the finished project has to deliver at least 55, the original value plus a tenth on top.

Those units are not guesswork. Ecologists measure them using the statutory biodiversity metric, a Defra tool that scores habitats on a range of things, including:

• Size

• Condition

• distinctiveness (how ecologically important the habitat type is),

• location.

A patch of species-rich grassland scores far higher than the same area of mown amenity lawn, which is why the quality of habitat counts as much as the acreage.

The starting point is always a baseline assessment: an ecologist surveys the site and records what habitat is already there, so the post-development figure can be compared against it.

Whatever is created or enhanced to hit the target has to be secured and managed for at least 30 years, usually through a planning condition, a Section 106 agreement, or a conservation covenant. Biodiversity units are the currency of the whole system, and once they are committed, they are committed for a generation.

How developers deliver the gain

There is a set order, the biodiversity gain hierarchy, for how a developer reaches that 10%.

On-site

What it means: Habitats are created or improved within the development's own boundary, through landscaping, planting or green infrastructure.

When it is used: First choice, wherever the space allows it.

Off-site

What it means: The developer buys biodiversity units from a habitat bank or landowner elsewhere, where new habitat has been created or restored.

When it is used: When the 10% cannot be met on the site itself.

Statutory credits

What it means: Units are bought directly from the government. They are priced deliberately high to discourage reliance on them.

When it is used: A last resort, when neither on-site nor off-site delivery works

Most real schemes land in the middle. Urban and high-density sites rarely have the space to hit 10% on-site, so developers buy off-site biodiversity net gain units from a habitat bank. A habitat bank is land where habitat is created or restored in advance, registered on the national Biodiversity Gain Sites Register, and split into units a developer can buy to discharge their planning condition.

As a rule, the further down the hierarchy a developer has to go, the more the gain tends to cost, which is why getting the approach right at the design stage matters.

Need off-site units for your scheme?

We hold live, registered biodiversity units across the region, ready to purchase.

See our available habitat banks

Why does biodiversity net gain matter?

For decades, development and nature pulled in opposite directions. Every new estate or road chipped away at the habitat with nothing put back. Biodiversity net gain flips that. It puts a number on nature, makes that number a planning requirement, and forces the gain to be real rather than a vague commitment in a design statement.

The effects run wider than wildlife:

• Nature recovery: more, bigger and better-connected habitats give species room to move and adapt.

• Climate resilience: new woodland and wetland lock up carbon, while green space cools towns and slows surface flooding.

• Healthier places: green space near homes is linked to better physical and mental health. Around nine in ten people in Natural England's surveys agree that natural spaces are good for wellbeing.

• A working market: landowners can now earn long-term income from creating habitat, and a supply chain of ecologists and habitat managers has grown around it.

For the people who deal with BNG day to day, it matters for a blunter reason. A scheme stalls without it. Handle the strategy early, and it is a manageable line in the budget. Leave it to the end, and it becomes a delay, a redesign, or a far bigger bill.

Sitting on land that could earn its keep? At Habitat Banks, we help landowners set up and register biodiversity gain sites.

Get in touch with our team

Who does the biodiversity net gain affect

Developers and planners

If you are building, biodiversity net gain for developers is now part of the application itself. You need a baseline habitat assessment, a biodiversity gain plan, and a credible route to your 10%. The earlier it feeds into site selection and design, the cheaper and simpler it is to deliver. Most developers who run into trouble do so because BNG was treated as an afterthought rather than a design input from day one.

Landowners and farmers

For landowners, biodiversity net gain for landowners is an income opportunity. Land that is marginal for farming can be turned into a habitat bank through restored grassland, new woodland, or wetland, and the resulting biodiversity units sold to developers who need them.

It is a long-term arrangement, tied to a 30-year management commitment, but it offers steady revenue that sits alongside existing farming and subsidies rather than replacing them. For many estates, it is the most productive use of their least productive ground, usually without taking it out of production. Working with landowners starts with assessing what the land could realistically deliver.

Biodiversity net gain in the West Midlands

Location is built into the metric. Off-site units carry more value when they are delivered near the development they offset, because the statutory biodiversity metric applies a spatial multiplier that reduces the worth of units created far away.

That is the gap biodiversity net gain that West Midlands providers work in. Habitat Banks West Midlands creates and manages habitat banks across Staffordshire, Birmingham / Black Country, Warwickshire and the wider region. We have woodland, heathland and grassland sites, some already live and available to purchase, and connect them with developers who need local, registered units to meet their obligations.

For landowners in the area, the same team sets up and registers biodiversity gain sites and partners in the long-term management that comes with them.

Habitat quality matters as much as proximity. Higher-distinctiveness sites, such as established and ancient woodland, can offset losses from a wider range of habitat types while still meeting the trading rules, which makes them useful for more developments. Matching units to the right local planning authority and national character area is part of getting an offset to stand up, and it is the detail that local providers are set up to handle.

Frequently asked questions on Biodiversity net gain

1. Is biodiversity net gain mandatory?

Yes. Mandatory biodiversity net gain has applied to major developments in England since 12 February 2024 and to small sites since 2 April 2024, with nationally significant infrastructure projects following from November 2026. Some developments are exempt, and the rules for minor and brownfield sites are being refined through 2026, so it is worth checking the current position for your specific scheme.

2. What are biodiversity units?

Biodiversity units are the unit of measurement in the statutory biodiversity metric. They come in three types, area, hedgerow, and watercourse, and these are assessed separately. You cannot offset the loss of a hedgerow by creating grassland; like must be replaced with like or better.

3. What is the difference between on-site and off-site BNG?

On-site gain is created inside the development boundary. Off-site gain is bought as off-site biodiversity units from a habitat bank or landowner elsewhere when the site cannot deliver the full 10% itself. Most schemes combine both.

4. When does biodiversity net gain apply?

It applies to most new planning applications in England, with some exemptions. Householder applications, genuinely tiny developments below the de minimis threshold, and certain other categories fall outside the requirement, and the exemptions are being updated through 2026. If a scheme needs planning permission and clears those thresholds, assume biodiversity net gain applies and check early.

5. How much do biodiversity units cost?

There is no single price. The cost of biodiversity units depends on the habitat type, its distinctiveness, the location, and how many units a scheme needs. High-distinctiveness habitats command more than common grassland, and government statutory credits are deliberately the most expensive route. The most reliable way to budget is to get the baseline assessment done and then price the shortfall against real off-site units.

6. What are some biodiversity net gain examples?

Biodiversity net gain examples include creating a wildflower area on a housing site, restoring neglected woodland, planting native hedgerows along a new road, or establishing a wetland beside a commercial development. Off-site, it usually means a landowner restoring grassland, woodland or other habitats to produce units for sale.

Getting biodiversity net gain right

BNG is not going away, and the projects that handle it well are the ones that plan for it early. If you are a developer who needs local, registered biodiversity units to discharge a planning condition, you can see the available habitat bank sites or tell us about your project and get a straight answer on what can be delivered and when.

If you are a landowner weighing up whether your land could generate units, that same conversation is the place to start.

Get in touch with Habitat Banks West Midlands, and we can point you in the right direction

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