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On-site vs Off-site Gains

Overview​

BNG can be delivered in three places, in order of preference: on-site (within the development's red line), off-site (elsewhere — the developer's own land or units bought from a habitat bank / landowner), and, as a last resort, statutory credits. This page is about the first two; credits get their own page.

The order is enforced by the biodiversity gain hierarchy.

Why it matters for BNG​

Where you deliver gain changes how much you must deliver, what it costs, and how long it takes to secure:

  • On-site gains keep biodiversity where the impact is, but compete with developable area. Every square metre of habitat is a square metre not built on.
  • Off-site gains free up the development footprint but attract a spatial risk multiplier and require legal securing and registration.
  • Both must be secured for 30 years; the mechanisms differ.

How it works: England​

On-site:

Off-site:

  • Gain delivered on other land, either the developer's own or purchased as biodiversity units.
  • Subject to a spatial risk multiplier in the metric: units delivered further from (and less connected to) the impact are discounted, nudging off-site delivery to be local and strategically sensible (see Strategic Significance).
  • Secured through a legal agreement (e.g. a conservation covenant or s.106) and recorded on the Biodiversity Gain Sites Register so a unit cannot be sold twice.

The metric enforces the hierarchy through these discounts and trading rules. It is generally more efficient to retain and enhance on-site than to recreate off-site, which is exactly the behaviour the scheme intends.

Verifying an off-site claim​

This is the one delivery route with a genuinely public, searchable check: the Biodiversity Gain Sites Register is a GOV.UK-hosted register that anyone can search to see which sites are registered as biodiversity gain sites, what habitat they are enhancing, and which development(s) their units have been allocated to. A planning or ecology team reviewing a metric that claims off-site units doesn't have to take the figure on trust. It can look the allocation up directly and confirm the units claimed against a development are actually registered, not just asserted in a spreadsheet.

The register is populated from what applicants submit, so it reflects allocations once an application has been accepted, not necessarily at the point a scheme is first proposed. A claimed off-site allocation on a live application may not yet appear on the public register even where it is entirely genuine. Absence from the register is therefore a prompt to ask when registration is expected, not automatic proof the units don't exist. On-site gains have no equivalent public register — their record is the planning permission, its conditions, and the HMMP itself.

Nation differences​

Unit-based on-site/off-site trading with a register is an England mechanism; see What is BNG?.

Off-site siting decisions draw on strategic and habitat data — the LNRS Local Habitat Maps and Habitat Networks layers inform where off-site units are most valuable.

WildStack's take​

WildStack's take

On-site gains sit inside a working development and can be quietly eroded over 30 years; well-chosen off-site gains on dedicated, managed land can be more secure and more ecologically coherent, even after the spatial discount. There is no universal right answer, but there is a universal wrong one: treating off-site units as a frictionless way to avoid designing nature into the scheme. The hierarchy exists to stop exactly that, and the spatial multiplier is its enforcement mechanism.

Official sources​

Last reviewed​

13 July 2026. Revisit if the spatial risk multiplier, the register, or the securing mechanisms change.

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