The cost of an unauthorised development put right

Putting an unauthorised development right costs more than doing it properly, and the largest item is rarely the application fee. On a converted property let without permission, the bill is typically the fee, professional fees, the cost of any works needed to make the scheme approvable, the rent lost while it is not lettable, and in the worst case the cost of undoing the work entirely.

There is also a timing rule that quietly removes your best option if you wait too long, and most landlords have never heard of it.

What a retrospective application actually is

Section 73A of the Town and Country Planning Act 1990 allows a planning application to be made for development that has already been carried out. It is an ordinary application in every other respect: same fee basis, same publicity, same consultation, same eight or thirteen week period, same right of appeal.

Carrying out development without permission is not in itself a criminal offence in most cases. It is a breach of planning control, and the council can take enforcement action. The criminal offences arrive later, for failing to comply with an enforcement notice, and immediately in the special cases of unauthorised works to a listed building or to a protected tree.

That distinction matters because it shapes the choice. You are usually deciding between commercial risks rather than between prosecution and safety.

The bill, item by item

Price all of it before deciding what to do.

Two of those catch people out. Measured surveys of a completed conversion cost more than drawings prepared before the work, because someone has to measure what was built rather than what was drawn. And the concession in the fees regulations that allows a further application without a further fee does not operate in the same way for development already carried out, so check the current regulations rather than assuming a second attempt is free.

The Building Regulations line is easy to forget entirely. Planning and building control are separate, and a regularisation certificate is a separate application with its own fee and its own inspection process, usually including opening up work.

Section 70C, and why timing matters

Section 70C allows a local planning authority to decline to determine a retrospective application where an enforcement notice has already been issued for the same development.

Read that again if you are considering waiting to see whether the council notices. Once the notice is issued, the ordinary application route can be closed off, and the only way to argue that permission should be granted is through an appeal against the notice on the ground that permission ought to be granted. That appeal brings a deemed application, and the fee regulations set a higher fee for it than for an ordinary application, so check the current figure before choosing that path.

The practical consequence is simple. If you know the development is unauthorised, apply before the council writes to you, not after. An application made voluntarily is a much better starting position than a notice you are trying to unpick.

Enforcement notices and the appeal route

If a notice arrives, the deadlines are short and unforgiving.

An enforcement notice specifies the breach, the steps required to remedy it, and a compliance period. It takes effect on a stated date unless an appeal is lodged before then, and lodging the appeal suspends it.

Appeals run on statutory grounds. The ones most often used are that planning permission ought to be granted, that the matters alleged do not constitute a breach, that the time for enforcement has expired, and that the steps required exceed what is necessary. Choose the grounds carefully, because each has its own evidence requirement and the deemed application fee attaches to the first of them.

On time limits, do not rely on the old four year rule for operational development or changes of use. The Levelling-up and Regeneration Act 2023 moved enforcement time limits in England towards a single ten year period, so establish the current position and the commencement date before deciding that a historic breach has become immune.

Failing to comply with an enforcement notice once the compliance period expires is a criminal offence, and for landlords there is a further exposure: where an unlawful use has produced income, confiscation proceedings under proceeds of crime legislation have been used to recover it. That is the scenario that turns a manageable planning problem into a serious financial one.

Selling, refinancing and the paper trail

Most unauthorised development is discovered by a buyer's solicitor rather than by a planning officer.

The clean answer is a lawful development certificate. Where the works or the use have become immune from enforcement, a certificate under section 191 confirms it, and a certificate is what a lender wants to see. Assemble the evidence while it exists: tenancy agreements, council tax records, utility bills, dated photographs, statutory declarations from people who can speak to the relevant period.

Indemnity insurance is the alternative offered on most transactions. It protects against the financial consequences of enforcement, but it does not make the development lawful, and it typically becomes void if you approach the council about the matter. Deciding between insurance and a certificate is a decision to take before contacting the council, not after.

Illustrative example: a landlord converts a shop with a flat above into three flats without permission. Four years later a purchaser's solicitor raises it. A retrospective application would have cost the fee and a set of drawings. By then the council had received a complaint and issued a notice, the section 70C position applied, and the case ran through an enforcement appeal with the associated fee and professional costs. The scheme was eventually permitted, with one flat lost to meet space standards.

Deciding between putting it right and applying

Work through four questions in order.

1. Is the development immune from enforcement? If it might be, pursue a lawful development certificate and gather the evidence first.
2. Would it have been permitted if you had applied? Take an honest view against the adopted local plan, not an optimistic one. Where the answer is yes, a retrospective application is straightforward.
3. What would make it permitted? Sometimes a modest change, such as reinstating a communal room, adding a bin store or obscure glazing a window, converts a refusal into an approval.
4. What is the cost of reversal? If reinstatement is inexpensive and approval is unlikely, undoing the work is often the rational answer.

Then prepare the application properly. A planning statement that addresses the policy tests directly, acknowledges the breach without excuses, and sets out the remedial work already done reads far better than one that pretends the situation is normal. Case officers deal with these regularly and they respond to candour.

This is general guidance rather than legal advice. Enforcement carries legal consequences, so take advice from a qualified professional and check the position with your local planning authority before acting.

If you are pricing the documents for a retrospective application, see PlanScope pricing or browse the 66 report types to see which the scheme is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.