How long can the council take enforcement action against unauthorised building work?

The law

(1) Where there has been a breach of planning control consisting in the carrying out without planning permission of building, engineering, mining or other operations in, on, over or under land, no enforcement action may be taken after the end of the period of: (a) in the case of a breach of planning control in England, ten years beginning with the date on which the operations were substantially completed,

The transitional provision keeps the 4-year limit for older breaches:

1. The amendments made to the 1990 Act by section 115 of the 2023 Act (time limits for enforcement) do not apply where: (a) in respect of a breach of planning control referred to in section 171B(1) of the 1990 Act (time limits), the operations were substantially completed, or (b) in respect of a breach of planning control referred to in section 171B(2) of the 1990 Act (time limits), the breach occurred, before the day on which that section comes into force.

"That section" is section 115, which came into force on 25 April 2024 (regulation 3(b)). So the test is the date of substantial completion, not the date work started. An extension started in March 2024 and finished in May 2024 is under the 10-year rule.

Two worked examples

• A rear extension built without permission and substantially completed on 10 June 2023. The 4-year limit applies. The period of four years beginning with 10 June 2023 ends at the end of 9 June 2027. After that the council cannot take enforcement action, unless an exception below applies.
• The same extension substantially completed on 10 June 2024. The 10-year limit applies. Enforcement remains possible until the end of 9 June 2034.

One consequence follows from the dates. The last building work that could benefit from the 4-year rule was finished on 24 April 2024, and its period ends at the end of 23 April 2028. From 24 April 2028, the 4-year rule will have run out for every breach it covers.

When the limits do not protect you

• A second attempt. Section 171B(4)(b) lets the council take further enforcement action within 4 years of earlier action on the same breach, even after the normal limit, for example to replace a defective notice.
• Deliberate concealment. Government guidance says that where a breach has been deliberately concealed, the council can apply for a planning enforcement order (section 171BA) allowing action after the limit, and that the courts have found the time limits do not engage until the breach is discovered.
• Listed buildings and conservation area demolition. No limit applies. See buying a listed building with unauthorised works.

Planning policy also changed. The National Planning Policy Framework published on 17 August 2026 says that where unauthorised development is shown to have been intentional, that fact should be given substantial weight in deciding a retrospective application (policy DM8).

What it means if you are buying

For any extension, loft conversion or outbuilding without permission, find out when it was substantially completed. If that was on or after 25 April 2024, it can be enforced against until well into the 2030s. The seller's argument that "it has been there four years" no longer works for newer work.

A local search shows enforcement notices and decisions. It does not show unauthorised work nobody has reported: see how to read a planning history.

Proving immunity: a certificate of lawful existing use

Once the limit has passed, and provided no enforcement notice is in force, the work is lawful for planning purposes (section 191(2)). The formal proof is a certificate under section 191. You must show, on the balance of probability, when the work was substantially completed. From 1 April 2026 the fee is the same as a planning application for the work: £548 for a householder extension. The council has 8 weeks to decide. See lawful development certificates.

Planning immunity says nothing about Building Regulations, which have their own enforcement rules, or about listed building consent.