What Happens If You Build Without Planning Permission in London? (2026)
The real consequences of building without planning permission in London — enforcement notices, the time limits for immunity, retrospective applications and how to put it right.
Plenty of London homeowners discover, often when they come to sell, that work they or a previous owner carried out never had the planning permission it needed. The consequences are more nuanced than the panic suggests: building without permission is a breach of planning control, not a crime, and councils have discretion over whether and how to act. But the risks are real — an enforcement notice can require work to be undone, and unauthorised work is a persistent problem at sale. This guide explains what actually happens when you build without planning permission in London in 2026, the time limits that matter, and the routes to putting it right.
The enforcement framework is national, but each borough exercises its discretion locally and the evidence of when work was done is specific to your property. We assess whether unauthorised work can be regularised or certified, and prepare the drawings a retrospective application or certificate needs, before anything is commissioned, free.
Is building without planning permission illegal?
Carrying out development without the required planning permission is a breach of planning control, but it is not, by itself, a criminal offence. The council can investigate and decide whether to take enforcement action, which is discretionary — it must consider whether the breach actually harms the area before acting. What does become a criminal matter is failing to comply with a formal enforcement notice once one has been served, or breaching the special controls that protect listed buildings and protected trees, where unauthorised work is an offence from the outset.
What enforcement action can the council take?
The council has a range of tools. It may invite a retrospective application to regularise the work, or serve a planning contravention notice to gather information. If it decides the breach is harmful, it can issue an enforcement notice specifying what must be done and by when — which can include altering or removing the work. A stop notice can halt ongoing work, and a breach of condition notice deals with broken planning conditions. Failing to comply with an enforcement notice is a criminal offence that can lead to prosecution and fines, and the council can carry out the works itself and recover the cost.
- Invitation to submit a retrospective application
- Planning contravention notice — to gather information
- Enforcement notice — requires the breach to be put right
- Stop notice / breach of condition notice; non-compliance is an offence
The time limits: when unauthorised work becomes lawful
Enforcement is time-limited, which is why the date work was done matters so much. Broadly, the council has four years from completion to act against unauthorised building operations, and ten years against most material changes of use. Once the relevant period has passed without enforcement, the development becomes immune and lawful, and a Lawful Development Certificate can confirm it. Note that recent reforms have been changing some of these periods, so the exact limit depends on when the breach occurred — dated evidence such as photographs, invoices and utility records is central to relying on immunity.
- Four years — unauthorised building operations (broadly)
- Ten years — most material changes of use
- After the period, the development becomes lawful (immune)
- Reforms have been adjusting periods — the date of the breach governs
How do you put unauthorised work right?
There are three main routes. If the work was in fact permitted development, or has become immune through the passage of time, a Lawful Development Certificate certifies that it is lawful — the cleanest outcome. If it did need permission and does not yet qualify for immunity, a retrospective (regularisation) planning application asks the council to grant permission after the fact; if granted, the work is authorised. If permission is refused and an enforcement notice follows, the work may have to be altered or removed, though there is a right of appeal. The right route depends entirely on the facts of the specific case.
- Lawful Development Certificate — if PD or now immune
- Retrospective application — asks for permission after the fact
- Alter or remove — if refused and enforced (with a right of appeal)
- The route depends on the facts and the evidence available
What does it mean for selling your home?
Unauthorised work is most often a problem at the point of sale, when a buyer's solicitor asks for the planning and building-control paperwork. Missing permission can stall or collapse a sale, reduce the price, or require indemnity insurance. The reassuring point is that it is usually fixable — with a Lawful Development Certificate where the work is lawful, or a retrospective application where it is not — provided it is dealt with rather than hidden. Sorting it before marketing the property is far smoother than discovering it mid-transaction. We assess the position and prepare whatever the chosen route requires.
How do you decide whether to regularise or wait for immunity?
When unauthorised work comes to light, the practical question is which route puts it right with the least cost and risk. That decision turns almost entirely on the facts of your specific case — what was built, when it was completed, whether it needed permission at all, and what evidence you can produce to prove the date. Getting this judgement right matters, because applying for the wrong thing wastes months and can even draw the council's attention to a breach it was not pursuing. The two questions below are the ones that decide the route in most London cases.
How strong is your evidence of the completion date?
If you intend to rely on time immunity, the whole case rests on proving when the work was finished and that it has been in place continuously since. Councils and the courts look for hard, dated evidence: photographs with verifiable dates, dated invoices and receipts, delivery notes, council-tax or utility records, and sometimes sworn statements from neighbours or tradespeople. Vague recollection is not enough. Where the evidence is strong and the relevant period has clearly passed, a Lawful Development Certificate for existing use is the clean route. Where the evidence is thin, relying on immunity is risky and a retrospective application is often safer.
Would the work get permission on its merits?
The second question is whether the development would actually be granted permission if assessed today. If it comfortably complies with the borough's policies — a modest extension within what would have been permitted anyway — a retrospective application is likely to succeed and regularises the position cleanly. If it plainly breaches policy and causes real harm, a retrospective application may be refused and could prompt enforcement, so it is worth taking a realistic view of the planning merits, and any professional advice, before deciding whether to apply, rely on immunity, or adjust the work first.
| Situation | Route | Outcome | Key evidence |
|---|---|---|---|
| Work was actually permitted development | Lawful Development Certificate | Certified lawful | Drawings vs PD conditions |
| Time immunity reached (4/10 years) | LDC (existing) | Certified lawful | Dated proof of completion |
| Needed permission, not yet immune | Retrospective application | Permission if granted | Plans + policy case |
| Refused and enforced | Comply or appeal | Alter/remove or overturn | Grounds of appeal |
Related services: Planning Permission, Lawful Development Certificate Drawings, Planning Drawings.
Frequently asked questions
What happens if you build without planning permission in London?+
Can I get planning permission after building work is done?+
How long before unauthorised building work becomes lawful?+
Does unauthorised building work affect selling my house?+
What evidence proves when unauthorised work was completed?+
Can the council make me demolish an extension built without permission?+
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