What Happens If You Build Without Planning Permission?

Published 15 April 2026

Building without planning permission - whether deliberate or accidental - is more common than you might think. Sometimes homeowners genuinely believe their project falls under permitted development. Other times, builders start work without checking the rules. Either way, the consequences can be serious.

This guide explains what happens when you build without planning permission, your options for regularising the situation, and the time limits that apply.

Is It Illegal to Build Without Planning Permission?

Strictly speaking, carrying out development without planning permission is not a criminal offence in itself. It is a breach of planning control under the Town and Country Planning Act 1990 (TCPA 1990). The council can take enforcement action to remedy the breach, but you won't be arrested simply for building an extension without permission.

However, it becomes a criminal offence if:

You fail to comply with an enforcement notice
You carry out unauthorised work to a listed building (this is a criminal offence from the outset under the Planning (Listed Buildings and Conservation Areas) Act 1990)
You breach a tree preservation order
You display an advertisement without consent (in certain circumstances)

What Is Enforcement Action?

If your council discovers unauthorised development, they have the power to take enforcement action. This is discretionary - councils don't have to take action, and many prefer to negotiate a solution first. But they can issue several types of notice:

Enforcement Notice

The most common form of action. An enforcement notice specifies the breach and requires you to remedy it within a set period (usually 28 days to several months). Remedying the breach could mean demolishing the structure, making alterations, or ceasing a particular use. Failing to comply is a criminal offence with unlimited fines.

Breach of Condition Notice

If you've built in accordance with a planning permission but breached one or more conditions attached to it, the council can issue a breach of condition notice. There is no right of appeal against these, making them a particularly powerful enforcement tool.

Stop Notice

In urgent cases, the council can issue a stop notice requiring work to cease immediately. These are relatively rare because the council is liable for compensation if the notice is later overturned on appeal.

Injunction

In the most serious cases, the council can apply to the courts for an injunction. This is typically reserved for persistent offenders or deliberate breaches where other enforcement methods have failed.

The 4-Year Rule and 10-Year Rule

Enforcement action has time limits. If the council does not take action within these limits, the development becomes lawful:

4-year rule: Applies to building work (including extensions) and change of use to a single dwelling. If the unauthorised development has existed for more than 4 years without the council taking enforcement action, it becomes immune from enforcement.
10-year rule: Applies to changes of use (other than to a single dwelling) and breaches of conditions. After 10 years, these become immune from enforcement.

Important change: The Levelling Up and Regeneration Act 2023 introduced provisions to extend the 4-year rule to 10 years for all types of breach. At the time of writing, the relevant regulations have not yet been brought into force, but this change is expected. Check current guidance from your local planning authority.

Certificates of Lawful Use

If your unauthorised development has exceeded the relevant time limit, you can apply for a Certificate of Lawful Existing Use or Development (CLEUD). This formally confirms the development is lawful. You'll need to provide evidence (photographs, statutory declarations, utility bills) proving the development has existed for the required period.

Retrospective Planning Applications

If you've built without planning permission and the time limit hasn't expired, your best option is usually to submit a retrospective planning application. This is a normal planning application submitted after the work has been done.

Key points:

The council assesses it on the same basis as any other application - the same planning policies apply
The application fee is the same as a prospective application
There is no penalty or additional fee for applying retrospectively
If approved, the development becomes lawful
If refused, you may need to remove or alter the development, or appeal the decision

Submitting a retrospective application does not prevent the council from taking enforcement action in the meantime, though in practice most councils will hold off while a retrospective application is being considered.

Impact on Selling Your Home

Unauthorised development can cause serious problems when you try to sell:

Conveyancing solicitors will check planning records and flag any development without a corresponding permission or LDC
Mortgage lenders may refuse to lend against a property with known planning breaches
Indemnity insurance can cover the risk in some cases, but only if no enforcement action has been initiated and the council hasn't been contacted about the breach
Buyers may demand a price reduction to reflect the risk

What Should You Do?

If you discover you've built without the required planning permission:

Don't panic. Many breaches can be regularised.
Check whether the work falls under permitted development. If it does, apply for a Lawful Development Certificate to confirm.
If it doesn't qualify as PD, submit a retrospective planning application. Get an architect or planning consultant to help you present the best case.
If the time limit has expired, apply for a CLEUD. Gather evidence of the development's existence over the required period.
If the council issues an enforcement notice, seek professional advice immediately. You have a right of appeal, but the deadline is strict.

Read more about planning permission basics or find your local planning authority to check enforcement policies in your area.