The 4-Year Rule Is Dead: New 10-Year Enforcement Rule for London Extensions
Since 25 April 2024, the old 4-year enforcement window for unauthorised building work has been replaced with a 10-year period. If you own a London property with an extension that was never properly approved, the risk has changed substantially.
Quick Answer
The 4-year rule no longer exists for new developments. Since 25 April 2024, councils have 10 years (not 4) to take enforcement action against unauthorised extensions and building work. For developments substantially completed before that date, the old 4-year rule still applies under transitional provisions. If you are unsure whether your extension is lawful, a Lawful Development Certificate (LDC) costs around £264 and gives you legal certainty.
4 years
Old enforcement window
10 years
New enforcement window
~£264
LDC application fee
Check your specific property constraints
Free Property CheckWhat Changed and When
Section 115 of the Levelling Up and Regeneration Act 2023 amended section 171B of the Town and Country Planning Act 1990. The change is simple: where the Act previously said "four" years, it now says "ten". This came into force on 25 April 2024.
Before this change, there were two enforcement time limits in planning law. Unauthorised building work (operational development) and conversion of a building to a single dwelling had a 4-year limit. All other breaches, such as changes of use and breaches of planning conditions, already had a 10-year limit.
Now there is a single 10-year limit for everything. The distinction between different types of breach no longer matters for enforcement purposes.
What the Old 4-Year Rule Was
Under the old rules, if someone built an extension without planning permission and the council did not take enforcement action within 4 years of substantial completion, the development became immune from enforcement. At that point, the owner could apply for a Certificate of Lawful Existing Use or Development (CLEUD) to formalise the position.
This created a well-known dynamic: some people built first and waited, knowing that if nobody complained for 4 years the work would become lawful by default. It was a calculated risk, and in many parts of London where council enforcement resources are stretched, it often worked.
Important distinction: The 4-year rule was never a "right" to build without permission. It was an enforcement time limit. The development remained technically unlawful throughout the 4-year period. The council could take enforcement action at any point during those 4 years, including ordering demolition.
The New 10-Year Rule
The principle remains the same but the window is 2.5 times longer. If you build without the required planning permission after 25 April 2024, the council now has 10 years to take enforcement action. Only after 10 years of continuous existence without enforcement does the development become immune.
Transitional provisions
The transitional provisions are significant. If you bought a house with an unauthorised extension that was completed in 2021, for example, the old 4-year rule applies and enforcement immunity would have been reached in 2025. But if the extension was completed in June 2024 (after the cut-off date), the 10-year clock applies and immunity would not arrive until 2034.
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Why This Matters for London Homeowners
London has an unusually high density of extensions, loft conversions, and outbuildings. Many were built decades ago without proper permissions, particularly in Victorian and Edwardian terraces. The change from 4 years to 10 years has several practical consequences.
Longer exposure period for new work
Anyone building without proper permission after April 2024 faces 10 years of risk instead of 4. That is 10 years during which a neighbour dispute, a council investigation, or a property sale could trigger enforcement action. A lot can happen in a decade.
Selling becomes harder
Conveyancing solicitors routinely check whether extensions have planning permission and building regulations approval. An unauthorised extension that is less than 10 years old is a red flag for buyers and their mortgage lenders. Previously, sellers could point to the 4-year immunity and move on. Now there is a much longer window of uncertainty.
Indemnity insurance is less reliable
Sellers of properties with unauthorised work often used indemnity insurance policies to satisfy buyers and lenders. These policies typically cost a few hundred pounds and cover enforcement action risk. But with a 10-year enforcement window, insurers face a longer risk period and premiums are likely to increase. More importantly, indemnity insurance only covers financial loss from enforcement action. It does not make the extension lawful or prevent a demolition order.
Mortgage lender scrutiny
Lenders worry that enforcement action could reduce the value of their security or leave the borrower unable to pay mortgage costs while dealing with compliance. With the enforcement period now 10 years, lenders may be more cautious about properties with unresolved planning status. Some may refuse to lend entirely without a Lawful Development Certificate or retrospective planning approval.
What Counts as "Unauthorised"
An extension or building work is unauthorised if it was carried out without the planning permission that was required, or if it exceeds what was permitted. Specifically:
- Built without planning permission where it was needed (not covered by permitted development)
- Exceeded permitted development limits (too deep, too high, too much site coverage, wrong materials)
- Breached conditions attached to a planning permission (different materials, altered design, missed landscaping requirements)
- Built in a conservation area, on a listed building, or in an Article 4 area without the specific permissions required
- Changed the use of the extension or building in a way that requires separate permission
Common misconception: Many homeowners assume that because their extension is within permitted development size limits, it is automatically lawful. This is not necessarily true. Permitted development has conditions beyond size, including materials, height relative to boundaries, site coverage, and restrictions in conservation areas and Article 4 areas. Breaching any condition means the entire development falls outside PD.
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When a council identifies unauthorised development, it has a range of enforcement tools. The severity depends on the nature and scale of the breach.
Enforcement notice
The most common tool. Requires the owner to remedy the breach within a specified period, which could mean demolishing the extension, altering it, or applying for retrospective permission. Failure to comply is a criminal offence.
Breach of condition notice
Used when planning permission was granted but conditions were not met. There is no right of appeal against a breach of condition notice, making it a particularly powerful enforcement tool.
Stop notice
Requires all building work to stop immediately. Used alongside an enforcement notice when the council considers the harm serious enough to warrant immediate cessation. Non-compliance is a criminal offence with unlimited fines.
Injunction
A court order restraining the breach. Councils use injunctions for serious or persistent breaches. Breach of an injunction is contempt of court, which can result in imprisonment.
Direct action
If an enforcement notice is not complied with, the council can enter the land and carry out the required works itself, then recover the costs from the owner. This can include demolishing an unauthorised extension and sending the owner the bill.
In practice, most London councils prefer negotiation over formal enforcement. They will typically invite a retrospective planning application before issuing an enforcement notice. But this is discretionary, not guaranteed. A neighbour complaint, a political priority, or a particularly egregious breach can fast-track formal enforcement.
Enforcement Activity Across London Boroughs
Enforcement activity varies enormously between London boroughs. Some councils have well-resourced enforcement teams and act proactively. Others are reactive and only investigate when a complaint is received.
Borough enforcement profiles
Enforcement activity levels can change with political priorities and council budgets. Do not assume your borough will not investigate.
The 10-year rule makes enforcement more likely over time, not less. A neighbour who was unaware of your extension for 3 years might discover it in year 7. Under the old rules, they would have been too late. Under the new rules, there are still 3 years of enforcement window remaining.
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How to Check If Your Extension Is Lawful
If you are unsure about the planning status of an extension on your property, whether you built it or it was there when you bought the house, there are clear steps to establish your position.
1. Check the planning history
Search your local council's planning portal for your address. All planning applications, decisions, and enforcement notices are public record. If you find an approval that matches the extension, you are likely fine. If there is no record of an application, investigate further.
2. Determine if it falls within permitted development
Even without a planning application, the extension may be lawful if it complies with permitted development rules. This depends on the size, height, materials, site coverage, and whether the property is in a conservation area or Article 4 area. An architect or planning consultant can assess this.
3. Apply for a Lawful Development Certificate (LDC)
This is the only way to get formal confirmation that your extension is lawful. There are two types: a certificate for existing development (CLEUD, confirming what is already built) and a certificate for proposed development (CLOPUD, confirming what you plan to build). The application fee for a householder CLEUD is around £264. The council must grant the certificate if the evidence shows the development is lawful, whether through permitted development compliance or enforcement immunity.
4. Pre-application enquiry
If you are unsure whether retrospective planning permission would be granted, a pre-application enquiry with your council gives you an informal indication of their likely decision before you submit a formal application. Fees vary by borough but are typically £200–£600 for householder enquiries.
Insurance and Mortgage Implications
The financial consequences of an unauthorised extension extend well beyond the planning system itself.
Buildings insurance
Most buildings insurance policies require the property to comply with planning and building regulations. An unauthorised extension may not be covered under your policy. If the extension causes or is involved in an insurable event (fire, subsidence, flood), the insurer could refuse the claim or reduce the payout. Check your policy wording.
Mortgage lending
Mortgage lenders require properties to have proper planning and building regulations approvals. An unauthorised extension less than 10 years old is a material concern. The lender's valuer will flag it, and the lender may refuse to lend, require a retention, or insist on an indemnity policy and/or retrospective approval before completing.
Indemnity insurance
A planning indemnity policy covers the financial cost of enforcement action (including demolition and loss of value). Premiums are typically £100–£500 and the policy runs for the life of the property. However, indemnity insurance has a critical limitation: contacting the council about the breach can invalidate the policy. And it does not make the extension lawful or prevent the council from taking action.
The Right Approach: Do It Properly
With a 10-year enforcement window, the calculation has changed fundamentally. The old gamble of "build it and hope nobody notices for 4 years" is now a 10-year bet against your neighbours, your council, and the property market.
Cost of doing it properly
Total cost of getting proper approval: £264–£4,600. Compare this to the cost of demolishing an unauthorised extension (easily £15,000–£40,000+), the collapse of a house sale, or a criminal prosecution for non-compliance with an enforcement notice.
If you have an existing unauthorised extension, take action now rather than later. If it is within permitted development limits, apply for a Lawful Development Certificate. If it is not, apply for retrospective planning permission. If retrospective permission is unlikely to be granted, get professional advice on your options before the council discovers the breach.
For new projects, there is no excuse. Confirm your permitted development rights with an LDC before you start, or get planning permission. The cost is a fraction of the build, and it removes all enforcement risk.
Frequently Asked Questions
Has the 4-year rule for planning been replaced?
Yes. Since 25 April 2024, the 4-year enforcement time limit for unauthorised building work has been replaced by a 10-year limit. This was enacted by Section 115 of the Levelling Up and Regeneration Act 2023, which amended Section 171B of the Town and Country Planning Act 1990. All breaches of planning control in England are now subject to a single 10-year enforcement period.
Does the 10-year rule apply to extensions built before April 2024?
No. Transitional provisions protect developments that were substantially completed before 25 April 2024. These still benefit from the old 4-year rule. However, any development that was not substantially completed by that date falls under the new 10-year rule. The key question is whether the building work was finished before the cut-off date.
What happens if I built an extension without planning permission?
The council can take enforcement action within the relevant time limit (4 years for pre-April 2024 completions, 10 years for later ones). Enforcement action can include an enforcement notice requiring alteration or demolition, a stop notice, an injunction, or direct action where the council demolishes the work and bills you. Non-compliance with an enforcement notice is a criminal offence.
Can I still get a Certificate of Lawful Development?
Yes. If your extension has been in place for longer than the applicable enforcement period (4 years for pre-April 2024 work, 10 years for later work) without enforcement action, you can apply for a Certificate of Lawful Existing Use or Development (CLEUD). You can also apply for a Certificate of Lawful Proposed Use or Development (CLOPUD) to confirm that planned work falls within permitted development before you start building.
How much does a Lawful Development Certificate cost?
The application fee for a householder Lawful Development Certificate is around £264 (as of 2025, fees are indexed annually). You will also need architectural drawings showing the development, which typically cost £500–£1,500 to prepare. The total cost of £764–£1,764 is minimal compared to the risk of enforcement action.
Can I sell a house with an unauthorised extension?
It is possible but difficult. The buyer's solicitor will identify the lack of planning approval during conveyancing. The buyer's mortgage lender may refuse to lend without an indemnity insurance policy, a Lawful Development Certificate, or retrospective planning permission. The 10-year enforcement window makes this more problematic than under the old 4-year rule, as the period of risk is substantially longer.
Will indemnity insurance protect me from enforcement?
Indemnity insurance covers financial losses from enforcement action (such as demolition costs or loss of property value) but does not prevent enforcement action or make the development lawful. Crucially, contacting the council about the breach without the insurer's consent can invalidate the policy. Premiums are typically £100–£500. It is a financial safety net, not a substitute for proper planning approval.
Which London boroughs are most active in planning enforcement?
Boroughs with large conservation areas and significant listed building stock tend to be most proactive, including Camden, Islington, Kensington and Chelsea, Richmond, and Westminster. However, all London boroughs will investigate complaints from neighbours or members of the public. Enforcement activity levels can change with political priorities and council budgets, so no borough should be assumed to be inactive.
Summary
The abolition of the 4-year rule is one of the most significant changes to planning enforcement in decades. For London homeowners, the message is clear: building without proper approval is now a 10-year gamble with serious financial and legal consequences.
If you are planning an extension, confirm your permitted development rights with a Lawful Development Certificate before you start, or apply for planning permission. The cost is trivial relative to the build.
If you already have an extension of uncertain status, do not ignore it. Check the planning history, assess whether it complies with PD rules, and if in doubt, get professional advice. Regularising the position now is always cheaper than dealing with enforcement later.
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