Statutory Designations and BNG
Overview
Some sites carry a legal protection that BNG does not touch. SSSIs, SACs, SPAs, Ramsar sites, and (differently) NNRs and LNRs each impose obligations that sit outside the 10% biodiversity net gain calculation. The single most important point on this page:
BNG units cannot discharge a designation obligation. A Habitats Regulations Assessment is not something you can "net gain" your way out of.
If a designation is in play, the designation question leads and the BNG number follows.
Why it matters for BNG
BNG and site protection answer different legal questions:
- BNG asks: does the scheme leave biodiversity ≥10% better off in metric units? It is an accounting target.
- Designation law asks: will the scheme harm this specific protected site's integrity/features? It is a gate, often with a much higher bar (up to "no adverse effect on integrity", subject to strict derogation tests).
You can pass the first and fail the second. Offering more biodiversity units does not offset harm to a designated site — the two currencies don't convert.
How it works — England
The designations, and where their teeth come from
| Designation | Legal basis (broadly) | Protection role |
|---|---|---|
| SSSI | Wildlife and Countryside Act 1981 | Core statutory site protection; underpins the higher designations |
| SAC | EU Habitats Directive → Conservation of Habitats and Species Regulations 2017 | Habitats/species of European importance (National Site Network) |
| SPA | EU Birds Directive → Habitats Regs 2017 | Wild birds (National Site Network) |
| Ramsar | Ramsar Convention 1971 + national planning policy | Wetlands (protected as habitats sites by policy) |
| NNR | 1949 Act / WCA 1981 | National importance + management; always also an SSSI |
| LNR | 1949 Act s.21 | Local importance; council-declared; usually not an SSSI |
The Habitats Regulations Assessment (HRA)
Where a plan or project could affect an SAC, SPA, or Ramsar site (a "habitats site"), a Habitats Regulations Assessment may be required under the Conservation of Habitats and Species Regulations 2017. In outline:
- Screening — is a likely significant effect possible? (The SSSI Impact Risk Zones are a common screening aid.)
- Appropriate assessment — if it can't be screened out, assess the effect on the site's integrity.
- Tests — the project may only proceed if it won't adversely affect integrity, or (exceptionally) passes strict derogation tests (no alternatives, imperative reasons of overriding public interest, compensatory measures).
Effects can arise from outside a boundary — via water, air, or recreational disturbance, and (for SPAs especially) via functionally linked land. That is why proximity, not just intersection, drives the screening.
Nation differences
The habitats-site regime and HRA derive from retained EU law and apply across the UK, but each nation administers its own designated sites and has its own SSSI- equivalent framework (e.g. Areas of Special Scientific Interest in Northern Ireland). BNG's mandatory metric is England-only; the designation obligations are not — a protected site in any nation carries its own regime regardless of whether BNG applies.
Related datasets
Every designation profile is linked in the table above. In WildStack's stack these drive planning-constraint triggers and briefing context, never habitat parcels: an SSSI IRZ or European-designation intersection raises a flag and enriches the briefing pack; the flag says "assess this", not "harm confirmed".
WildStack's take
The most expensive misconception in BNG practice is that a strong net-gain offer can soften a designation problem. It cannot — and pitching it that way to a regulator can actively damage a case, because it signals a misunderstanding of the law. BNG and HRA are different currencies: one is metric units, the other is "no adverse effect on site integrity", and there is no exchange rate between them.
Our discipline in a desk-based assessment is to separate the two questions explicitly. First: is a designation in potential play (including via proximity, water, air, or functionally linked land)? If yes, that is an HRA/consultation matter for an ecologist, full stop. Only then do we talk about the metric. Getting the order right saves clients from spending on a 10% solution to a problem the 10% can't solve.
Official sources
- Habitats regulations assessments: protecting a European site — GOV.UK
- Protected sites and areas: how to review planning applications — GOV.UK
- The Conservation of Habitats and Species Regulations 2017 — legislation.gov.uk
Last reviewed
5 July 2026. Revisit if the Habitats Regulations 2017 are amended, if the National Site Network framework changes, or if the relationship between BNG and protected-site consenting is clarified in policy or case law.