Ten year enforcement time limit and proving immunity

The enforcement time limit is ten years for every kind of breach of planning control in England, following the change made by the Levelling-up and Regeneration Act 2023 and brought into force on 25 April 2024. The four year rule that used to cover operational development and the change of use of a building to a single dwelling has gone for anything happening on or after that date. For a landlord holding a converted property, an unauthorised annexe or a flat created without permission, that doubles the period of exposure.

The position described here is as at September 2026. Enforcement provisions have moved repeatedly since 2023, so check the current wording of section 171B of the Town and Country Planning Act 1990 and the relevant commencement regulations before relying on a date.

What the four and ten year rules used to do

Section 171B set three periods. Operational development, meaning building, engineering, mining or other operations, became immune four years after the development was substantially completed. The change of use of a building to use as a single dwellinghouse also carried a four year limit. Everything else, including other changes of use and breaches of condition, carried ten years.

That structure produced some odd results. An unauthorised rear extension was safe after four years while the unauthorised use of the same building as two flats took ten. A garage converted to an independent dwelling was immune in four years, while the same garage used as a hairdresser needed ten.

Landlords relied on the four year rule constantly, usually without naming it. The outbuilding let as a studio, the loft turned into a fourth bedsit, the side extension built without a certificate: all of it became unchallengeable relatively quickly.

What changed, and from when

The 2023 Act replaced the four year periods with a single ten year period for England. Wales retains its own position, so this is an England-only change.

The transitional treatment is the part to get right. Where operational development was substantially completed before the change took effect, or a change of use to a single dwellinghouse occurred before it, the old four year period continues to apply. So a rear extension finished in 2022 still became immune in 2026 on the old basis, while one finished in May 2024 runs to 2034.

The date that matters for operational development is substantial completion, not the start of works and not the date of the building control final certificate, although the latter is useful evidence of the former. For a change of use it is the date the use began, judged on the facts rather than on when anyone noticed.

Our overview of the reform itself sets out how it fits with the other enforcement changes in the same Act, including the move to ten years.

Breaches that never become immune

Immunity is narrower than people assume, and three categories sit outside it entirely.

Listed building works carried out without consent have no time limit. Unauthorised alteration of a listed building remains open to enforcement indefinitely, and the criminal offence under the listed buildings legislation has no equivalent of the ten year rule.

Works to protected trees are similarly unforgiving. Felling or lopping a tree covered by a tree preservation order, or a tree in a conservation area without notice, remains an offence regardless of elapsed time.

Deliberate concealment is handled by the planning enforcement order provisions in sections 171BA to 171BC, added after a case where a dwelling was hidden behind hay bales. Where a breach has been deliberately concealed, a magistrates' court can authorise enforcement action outside the normal limit. Concealment means more than nobody noticing; it means positive steps to hide the development.

Enforcement warning notices and what they signal

The 2023 Act also introduced enforcement warning notices. An authority serving one is telling you that it considers there has been a breach, that there is a reasonable prospect permission would be granted if applied for, and that you should apply within a stated period.

A warning notice does not itself require anything to stop and does not extend any time limit. Treat it as an invitation with a deadline attached, because what follows if the invitation is declined is usually an enforcement notice. Where the breach is likely to be acceptable in policy terms, the retrospective application costs less than the alternative, and the supporting Planning Statement is the document that carries it.

Proving immunity when you need to

The formal route is an application for a certificate of lawful existing use or development under section 191 of the 1990 Act. The burden of proof sits on the applicant, and the standard is the balance of probabilities.

The leading principle, from the Gabbitas line of cases, is that an applicant's own evidence can be enough if it is precise and unambiguous, and that a council cannot simply refuse because the evidence is uncorroborated. In practice councils look for a bundle:

• A statutory declaration from the person with direct knowledge, dated and witnessed properly.
• Council tax records showing separate banding from a specific date.
• Tenancy agreements running continuously through the period, with gaps explained.
• Utility accounts in occupiers' names, or meter installation records for a separate supply.
• Dated aerial or street-level imagery showing the physical change.
• Bank statements showing rent received, redacted as necessary.
• Contractor invoices and building control records for the works themselves.

Continuity is what fails applications. A ten year use broken by an eighteen month vacancy invites an argument that the use was abandoned, and abandonment turns on the period of non-use, the owner's intentions, any intervening use and the physical condition of the building. Document the quiet periods rather than skipping over them.

The same evidence supports ground (d) on an enforcement notice appeal, which is that no enforcement action could be taken at the date the notice was issued. Running a certificate application and holding ground (d) in reserve is normal practice, and the certificate route is cleaner because it produces a document a lender and a buyer can read.

Due diligence after the change

For anyone buying converted stock, the ten year rule changes the questions to ask.

1. Establish the date each unit was created, with documentary evidence rather than the vendor's recollection.
2. Check whether that date falls before or after 25 April 2024, because the applicable period differs.
3. Look for building control records, which fix dates better than anything else available.
4. Ask whether a certificate of lawful existing use has ever been applied for, and whether one was refused. A refusal sits on the planning record.
5. Where the position is unclear and the property is being bought on its converted income, price the risk or make the certificate a condition of completion.

And do not assume a long-standing use is safe because nobody has complained. Complaints arrive when a neighbour changes, and a use that has run for eight years is now two years short rather than four years clear.

One honest uncertainty: how authorities will apply the transitional provisions to development completed in stages is not settled, and substantial completion of a phased conversion can be argued either way. Where a scheme straddles April 2024, get advice before making a certificate application, because a refusal is a matter of public record.

Follow reform news on the planning law timeline, and read our note on commencement and completion notices for the other side of the same Act, which is what happens when a permission is started but never finished.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A certificate of lawful development is the only formal way to confirm that works or a use are lawful. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.