Checking an off-site unit on the biodiversity gain sites register

The biodiversity gain sites register is the public record of every off-site habitat scheme that can be counted towards the statutory 10 per cent gain in England. Natural England maintains it under Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. If you are buying off-site units, the register is where you confirm the site exists, the habitat works are legally secured, and the units you are paying for have not already been sold to someone else.

Buyers still turn up at gain plan stage with an invoice and no register entry. That is the wrong order.

What the register records

An entry is not a marketing listing. It records the land itself, by boundary and grid reference, together with the biodiversity value of that land before the works and the value those works are expected to reach. Values are split into the three currencies the statutory metric uses: area habitat units, hedgerow units and watercourse units. They are not interchangeable.

The entry also records the legal mechanism holding the habitat works in place for at least 30 years, the responsible body or local planning authority on the other side of that mechanism, and the habitat management and monitoring plan. Finally it records allocations: which developments have claimed which units.

That last field is the one buyers skip. An entry showing ten area habitat units created does not mean ten are available.

Searching for a site and reading the entry

Search by location first. The register lets you look for gain sites by area, and the distance from your development matters because of how the statutory metric treats spatial risk. The metric reduces the value of units delivered further from the development site, so a unit created outside your local planning authority area and outside the same national character area is worth less than its headline figure. Check the multiplier in the version of the metric current when your gain plan is submitted, because the metric is revised.

Then read the habitat detail. Trading rules in the metric require like for like or better. Units created as modified grassland cannot substitute for the loss of a species-rich grassland, and no amount of unit arithmetic gets around that. A Biodiversity Net Gain Assessment that shows a shortfall in one distinctiveness band has to be met by units in that band or higher.

Cross-check the site's surroundings while you are there. Designations, priority habitat and irreplaceable habitat near a gain site change what the responsible body will accept, and our guide to checking designations around a site on MAGIC covers the layers worth looking at.

How an allocation to a development works

Allocation is a formal step taken by the gain site owner, not by the developer. The owner applies to record on the register that a stated number of units from their site is allocated to a specific development, identified by its planning permission reference and local planning authority.

A single gain site can be allocated across many developments, in slices, until its units are exhausted. This is why the ordering matters: an allocation to your permission is the only thing that ties those units to you on the public record. A contract with the landowner is a private promise. The register entry is the evidence the local planning authority will look at when it considers your biodiversity gain plan.

Ask for the allocation to be recorded before final payment, or structure payment so the balance falls due on allocation.

Checking the securing mechanism

Off-site gains are secured either by a conservation covenant with a responsible body designated by the Secretary of State, or by a planning obligation under section 106 with the local planning authority for the area where the gain site sits.

Both work. They behave differently.

A conservation covenant binds successors in title and is enforced by the responsible body, which has its own monitoring obligations and its own charging structure. A section 106 agreement is enforced by the council, which may or may not have capacity to monitor a habitat 30 years out. Ask which mechanism applies, ask to see it, and check that the habitat works described in the agreement match those described in the register entry and in the habitat management plan. Mismatches between those three documents are common on early gain sites.

Check too that the responsible body named in a covenant appears on the government's published list of designated bodies. A covenant with an organisation that is not designated does not do the job.

Due diligence on the land and its management

The baseline condition of a gain site is assessed by survey, and the assessment must be carried out by a competent person. The Environment Act 2021 regime treats biodiversity net gain as work for a qualified ecologist, and a metric completed without a proper habitat condition assessment is the single weakest point in most off-site offers. Ask for the survey, the survey date and the surveyor's qualifications, and check the condition scores against the habitat descriptions rather than taking the output figures on trust.

Things worth confirming before you commit:

• Who holds the long-term management liability, and whether it is funded or merely promised.
• Whether the management plan has a monitoring schedule with reporting to the responsible body.
• Whether the habitat creation has actually started, or whether the units are being sold against habitat that exists only on paper.
• Whether any part of the site is already subject to another environmental obligation, such as nutrient mitigation or an agri-environment agreement, which cannot be double counted.
• What happens if the habitat fails to reach its target condition at year 10 or year 20.

A Preliminary Ecological Appraisal of your own development site should be finished before you go shopping for units, because it tells you which habitats you are actually losing and therefore which units you need.

Timing against gain plan approval

The biodiversity gain condition is deemed to be attached to most planning permissions in England. It requires a biodiversity gain plan to be submitted to and approved by the local planning authority before development begins. The plan identifies the on-site gains, any registered off-site gains allocated to the development, and any statutory biodiversity credits purchased from the government.

Work backwards from that. The register allocation has to be in place before the gain plan can rely on it, the metric has to be completed against the version current at the time, and the authority has its own period to determine the plan. Leaving this to the month before a start on site is how schemes slip a quarter.

Statutory credits exist as the last resort in the hierarchy, and they are priced to be the expensive option. Treat them as a fallback rather than a plan.

When an allocation falls through

Allocations can be reversed, and gain sites can fail. If the habitat works are not delivered, or the securing mechanism is found to be defective, the units disappear and the condition still has to be discharged.

Three responses are available: find and allocate replacement units on another registered site, buy statutory credits, or revise the scheme to reduce the off-site requirement. All three cost money and time, which is the argument for spreading a large off-site requirement across more than one gain site rather than relying on a single supplier.

Biodiversity net gain is a report type where a competent person is legally required, so treat any AI-assisted draft as the starting point for that ecologist rather than a substitute. You can find reviewers through the professional directory.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.