Retrospective planning options after starting work

If the extension is already built and it turns out to be larger than the permitted development limits allow, there are three retrospective planning application options and they are not interchangeable. You can apply for planning permission for development already carried out under section 73A of the Town and Country Planning Act 1990. You can apply for a certificate of lawfulness under section 191 if the works are immune from enforcement because of the passage of time. Or you can wait, which only works if you understand the enforcement time limits and are willing to live with the consequences while they run.

Nothing happens automatically. The council does not have to notice, and it does not have to act when it does.

What happens when works exceed the limits

Permitted development is a grant of permission subject to limits and conditions. Exceed a limit by a single centimetre and the whole development falls outside the class, which means it is unauthorised rather than partly authorised. A rear extension 400 millimetres too deep is not a lawful extension with an unlawful strip on the end.

The breach is not a criminal offence in itself for ordinary development. Carrying out development without permission is a breach of planning control, and the council may take enforcement action, but it is not obliged to. Enforcement is discretionary and most authorities apply a published policy weighing harm, expediency and the public interest.

Works to a listed building are different. Unauthorised works affecting the character of a listed building are a criminal offence under the Planning (Listed Buildings and Conservation Areas) Act 1990, prosecution is possible, and consent can be granted after the event but the offence does not disappear because consent follows.

Retrospective applications under section 73A

Section 73A allows an application for planning permission for development already carried out, whether carried out without permission or in breach of a condition. The application is made on the same forms, carries the same fee, is publicised in the same way and is decided on the same policy basis as a prospective one.

Two features of the process matter. The fact that the works exist is not a material consideration in favour of permission, so do not argue that removing them would be wasteful. And the application is decided against current policy, which may be more or less favourable than the policy in force when the works were built.

What does help is evidence of acceptability on the merits: a daylight study answering an overshadowing objection, a measured survey showing the actual relationship to the boundary, and a design response such as changing a window to obscure glazing or reducing a parapet. A Planning Statement that addresses the objections squarely, rather than apologising, is the right approach.

If permission is refused, there is a right of appeal under section 78, and the works stay up while the appeal runs unless an enforcement notice is also in force.

Lawful development certificates for completed works

Where the works have been in place long enough to be immune from enforcement, the route is a certificate of lawfulness of existing use or development under section 191. The certificate does not grant permission. It records that the development is lawful and cannot be enforced against, which is what a buyer's solicitor needs.

The burden of proof is on the applicant, and it is the applicant's own evidence that matters. What tends to persuade: dated photographs with verifiable context, council tax or utility records, invoices and contracts from the builder, aerial imagery, and statutory declarations from people with direct knowledge. Thin evidence fails, and a refused certificate tells the council exactly where the breach is.

A certificate under section 192, for proposed works, is the preventive version and worth using before building anything marginal.

Enforcement notices and the appeal grounds

If the council decides to act, the usual instrument is an enforcement notice specifying the breach, the steps required and the period for compliance. It takes effect after a stated date and, once effective, non-compliance is an offence.

An appeal against an enforcement notice goes to the Planning Inspectorate and must be made before the notice takes effect, which is a hard deadline. The grounds are set out in section 174 and include that planning permission ought to be granted, that the matters alleged have not occurred, that there has been no breach of planning control, that enforcement is time barred, that the notice was not properly served, that the steps required exceed what is necessary, and that the compliance period is too short.

Ground (a), that permission ought to be granted, carries a fee and effectively runs a retrospective application through the appeal. Combining grounds is normal, and the Inspectorate can vary a notice rather than quashing it.

A breach of condition notice is the alternative instrument for condition breaches, and there is no appeal against it, which is why it is used.

Immunity periods and the current limits

England moved to a single ten-year limit. Under changes made by the Levelling-up and Regeneration Act 2023, which took effect on 25 April 2024, the period for taking enforcement action is ten years for breaches occurring on or after that date, replacing the previous four-year rule for operational development and for change of use to a single dwellinghouse.

Breaches substantially completed before that date generally keep the four-year period, which means the two regimes run side by side for some years. Check the current position before relying on either, because transitional provisions of this kind are the ones most often misunderstood.

Deliberate concealment can extend the position further, since the courts and the legislation both allow for action where a breach has been concealed, so a building hidden behind a hoarding does not quietly become lawful on schedule.

Selling a property with unauthorised works

The problem surfaces on sale. A buyer's solicitor raises an enquiry, the seller cannot produce a permission or a certificate, and the transaction stalls at the worst possible moment.

Three options exist. Apply for a certificate if the works are old enough, apply retrospectively if they are not, or offer an indemnity policy. Indemnity insurance covers the financial loss if the council takes action, and it costs less and takes less time than an application. But it has real limits: insurers will not write a policy where the council already knows about the breach, where correspondence has started, or where an application has been made and refused, and a policy does not make the works lawful.

So the order of operations matters. Do not contact the council to ask about a potential breach before you have taken advice, because the enquiry itself can make a policy unavailable. Our notes on the curtilage rule for garden outbuildings and on garden offices and the separate planning unit problem cover two of the breaches that most often emerge at this stage.

Building regulations are a separate regime with its own remedy, a regularisation application to the building control body, and a planning permission does nothing for a building regulations breach.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and remember that a lawful development certificate under section 191 or 192 is the only formal way to confirm that works are lawful.

To draft the supporting statement for a retrospective application, enter your postcode on PlanScope and answer the guided questions about the works already carried out.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.