Immunity from enforcement: the four and ten year rules

Enforcement immunity in planning is a time bar, not an approval. Once the relevant period has run without the council taking enforcement action, the breach becomes lawful and no enforcement notice can be issued. For breaches in England the position changed under the Levelling-up and Regeneration Act 2023, which set a single ten year period in place of the old four and ten year split. The change applies going forward, so which rule governs your situation depends on when the breach happened.

That transitional point is the whole game for a landlord holding an unauthorised flat conversion or an outbuilding that has been there for years.

Where the time limits sit

Section 171B of the Town and Country Planning Act 1990 sets the periods after which no enforcement action may be taken. It is the only place the rule lives, and it operates automatically. There is no application to make and no certificate required for immunity to arise, although a certificate is the sensible way to prove it.

The section works by reference to the date of the breach. For operational development the period runs from substantial completion. For a change of use it runs from the date the use began. For a breach of condition it runs from the date the breach began, and a use or condition breach that stops and restarts can reset the clock.

The old four year rule

Under the position that applied before the 2023 Act change, four years applied to two categories.

The first was operational development: building, engineering, mining or other operations. Four years from substantial completion, after which the building was immune.

The second was the change of use of any building to use as a single dwellinghouse. That covered the classic case of a barn, an office or an outbuilding converted to a house without permission and lived in for four years.

Everything else fell into the ten year category, which is why the conversion of a house into flats, or into a house in multiple occupation beyond the permitted class, attracted the longer period even though the works looked similar.

The ten year rule

Ten years applied, and now applies generally in England, to any other breach: changes of use other than to a single dwelling, and breaches of condition.

Breach of condition cases are the ones landlords meet most often. A permission granted with an occupancy restriction, an agricultural tie, a holiday-use condition or a restriction on the number of bedrooms is breached the day the property is used otherwise, and the period runs from then, provided the breach is continuous.

Continuity is the pinch point. A holiday let condition breached for eight years, complied with for a season, then breached again does not give you ten continuous years.

What the 2023 Act changed

The Levelling-up and Regeneration Act 2023 amended section 171B so that in England a single ten year period applies to all breaches, removing the four year rule for operational development and for change of use to a single dwelling. The change took effect in 2024 and applies to breaches occurring on or after the commencement date.

Two consequences follow, and both need checking against the commencement order rather than assumed.

A breach that had already become immune under the old four year rule before commencement keeps that immunity. Immunity once acquired is not taken away.

A breach that began before commencement but had not yet run its four years is the harder case, and the transitional provisions are what decide it. As at September 2026, take the commencement and transitional wording from the legislation itself and, where the dates are close, take advice. Getting this wrong means applying for a certificate a year too early and telling the council exactly where to look.

Deliberate concealment

Immunity is not available to someone who hid the breach. The courts have held that a person who deliberately conceals unauthorised development cannot rely on the time limits, and Parliament added a mechanism to the same effect.

A local planning authority can apply to a magistrates' court for a planning enforcement order where there has been deliberate concealment. If granted, the order opens a further period in which enforcement action can be taken, even though the ordinary time limit has expired.

Concealment means more than not telling anyone. It means positive steps: false statements to the council, works hidden behind a facade, a building disguised as something else. Simply building without permission and waiting is not concealment, but a landlord who submits misleading information in a certificate application is on very different ground.

What immunity does not give you

Immunity bars enforcement. It does not turn the development into a permission, so there are no conditions to comply with and nothing to discharge, and equally nothing that regularises the position for other regimes. Building control approval is a separate question, as is fire safety in a converted block, and a mortgage valuer will ask about both.

It also attaches to the development as it stands. Extend the immune outbuilding, or intensify the immune use, and the new element starts its own clock.

Proving continuous use

The evidence burden falls on whoever asserts immunity, on the balance of probabilities, and the file has to cover the whole period without gaps.

Assemble it around a timeline rather than a folder of documents:

• Statutory declarations from the applicant and from independent witnesses, each stating what they saw and when.
• Tenancy agreements, rent records and licences covering each year.
• Council tax and utility accounts, including the void periods.
• Dated photographs and aerial imagery for operational development.
• Business records, insurance and delivery notes for a commercial use.

Where a gap exists, address it. A void between tenancies of a few weeks is not a break in the use of a building as flats. A property boarded up and empty for two years may well be, and the honest position is that the case law here is fact-specific.

The formal route to prove immunity is a lawful development certificate for an existing use or operation, which the council must issue if the evidence makes out the case. The supporting planning statement should walk the officer through the timeline year by year rather than leaving them to assemble it.

Heritage is different

None of this applies to unauthorised works to a listed building. Carrying out works that affect the character of a listed building without consent is a criminal offence, and the enforcement regime for listed buildings does not give the same immunity by lapse of time. A conservation area consent breach, works to a protected tree and advertisement control all have their own rules too.

So a landlord who has removed original panelling or replaced windows in a listed building cannot rely on ten quiet years. Where the works also affect the setting of a heritage asset, a listed building enforcement notice can require reinstatement long after the planning position would have settled, and the evidence needed to resist one is a heritage statement rather than a bundle of utility bills.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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