The Date That Decides: Proving Immunity from Planning Enforcement in 2026

The question behind the question

When a buyer, lender or insurer asks whether a property has planning problems, the immediate question is usually about permissions. The more revealing question is often about dates. An extension built without consent, a house converted from a barn, or a use that has quietly persisted for years may look irregular on paper. Whether it remains vulnerable to enforcement depends on how long the breach has existed and whether that history can be proved.

In England, the statutory framework is found in the Town and Country Planning Act 1990. The key provision, section 171B, sets two principal time limits. They are not arbitrary. They reflect a long-standing policy that planning authorities should not be able to pursue every historical irregularity indefinitely, while still allowing action against recent and concealed breaches.

Two clocks, not one

The first limit is four years. It applies to unauthorised operational development — building works such as extensions, outbuildings and alterations — and to the change of use of a building to use as a single dwellinghouse. Once four years have passed from the date the breach occurred, enforcement action is generally time-barred.

The second limit is ten years. It is the default for other breaches of planning control. That includes many changes of use, breaches of planning conditions, and failures to comply with the terms of a permission. The ten-year period is not a safety net for every irregularity; listed building works, conservation area demolition and some other heritage matters sit under different regimes and should not be assumed to follow the same timetable.

The distinction matters because a project can contain more than one breach. A conversion that creates a single house may attract the four-year rule, while a separate change of use on the same site may fall within the ten-year default. Mixed and continuing breaches require a careful reading of what was done, when it was done, and whether the breach is complete or ongoing.

Why the dwellinghouse rule attracts attention

The four-year rule for a change of use to a single dwellinghouse is well known, but it is often applied too loosely. It does not mean that any residential conversion becomes lawful after four years. It applies to the use of a building as a single dwellinghouse. A conversion into flats, a mixed residential and commercial use, or a dwelling created as part of a wider operational development may engage different rules.

The date of breach is also less obvious than it appears. For a change of use, the clock generally starts when the new use begins. For building works, it starts when the works are substantially complete, not when they are started. Proving either date years later requires evidence that is independent, contemporaneous and consistent.

Concealment does not stop the clock in the way people assume

There is a common belief that hiding an unauthorised development prevents time from running. That is too simple. The statutory time limits are not generally suspended merely because a breach was concealed. What concealment does is make the factual position harder to establish. It can also affect the credibility of an application for a lawful development certificate, and it may expose a person to other consequences if false or misleading information is given.

In practice, concealed breaches are often the ones that generate the most risk. A local authority may have had no opportunity to inspect the site, and the evidence of when the use or works began may rest entirely on the owner’s account. That is not a comfortable position for a buyer. The absence of enforcement action is not proof of immunity; it may simply mean the authority has not yet formed a view.

The certificate is the evidence, not a favour

A lawful development certificate, usually called an LDC, is the formal way to establish that a breach has become immune from enforcement. Applications are made under section 191 of the 1990 Act for existing development. The certificate confirms the lawfulness of the development described in the application on the date of the decision.

An LDC is not retrospective planning permission. It does not authorise future changes, and it does not cure every defect. But it is powerful evidence for a buyer, lender or insurer. A certificate granted on the basis of accurate information gives a degree of certainty that an enforcement notice cannot simply be served later.

The application must be supported by a plan and a clear statement of the breach, together with evidence showing when it began. Local authorities are entitled to test that evidence. A thin application supported only by a letter from the seller is likely to attract a request for more information or a refusal.

The paper trail that decides the point

Good evidence usually has three qualities: it is dated, it is independent, and it tells a consistent story. Useful material may include historical aerial photography, dated photographs showing the works under construction, building control records, utility accounts, council tax records, electoral roll entries, invoices from contractors, planning history files, and correspondence with the local authority.

Statutory declarations from previous owners or neighbours can help, but they carry less weight if they are vague or prepared solely for the sale. A bundle of documents that cross-refers — for example, an invoice for roof works, a dated photograph of the completed roof, and a utility bill for the occupied building — is far stronger than a single assertion.

For buyers, the due diligence process should include a local land charges search, the standard CON29R enquiries, a review of the planning register and enforcement register, and direct questions to the seller about any works or uses that may have taken place without consent. Planning indemnity insurance may be offered, but it is not a substitute for establishing the facts. Policies can be difficult to claim on and may not satisfy a lender if the underlying breach is unresolved.

What to do before exchange

Where an irregularity is identified, the safest course is usually to obtain an LDC before completion. If that is not possible, the buyer should understand precisely what is being relied on, who prepared the evidence and whether the seller will provide a warranty or retain liability. The price should reflect the risk if the position remains unproven.

At Thornbury Plan, the practical message for 2026 is straightforward. Time limits can convert a planning breach into a lawful state, but they do not do so automatically. The date of breach must be established, the evidence must withstand scrutiny, and the certificate should be in hand before the property changes hands. An irregular past is not always a dealbreaker. An undocumented one frequently is.