You've built something - or you've bought a house where something was built - and now you're realising it might not have had planning permission. Maybe a builder told you it was fine. Maybe you assumed it was permitted development. Maybe you inherited the problem when you bought the property. However you got here, you need to know what happens next.
The good news: you can apply for planning permission after the work has been done. This is called a retrospective planning application. The council assesses it exactly as they would a normal application. If the work would have been approved, it usually will be. The bad news: if it's refused, you may have to undo it.
First: a planning breach is not a criminal offence. Building without planning permission is not illegal. What is illegal is failing to comply with an enforcement notice once one has been issued. Until that happens, you have options and time to resolve the situation.
Second: many projects that homeowners worry about turn out to be permitted development after all. A rear extension, a loft dormer, a garden office - these may not have needed planning permission in the first place. Before you apply for retrospective permission, it's worth checking whether the work actually falls within the PD rules. If it does, you can apply for a Lawful Development Certificate (£274) instead - a simpler, cheaper process that confirms the work is lawful.
A planning breach is not a criminal offence. You have time and options to resolve it.
A retrospective planning application is submitted through the Planning Portal in exactly the same way as a standard application. You pay the same fee - currently £548 for a householder application as of April 2026. You submit the same drawings and documents. The council assesses it against the same planning policies.
The key difference is that the work already exists. The council isn't deciding whether to let you build - they're deciding whether what you've built is acceptable. If it is, permission is granted. If it isn't, permission is refused and the council can issue an enforcement notice requiring you to modify or remove the work.
There is no penalty or surcharge for applying retrospectively. The fee and process are identical to a normal application.
Think the work might actually be permitted development? A free eligibility check can help you understand whether you need planning permission at all.
Local authorities have a limited time to take enforcement action against planning breaches. Since 25 April 2024, a single 10-year rule applies to all breaches of planning control in England.
If unauthorised development has existed continuously for 10 years without enforcement action, it becomes immune from enforcement. At that point, you can apply for a Certificate of Lawful Existing Use or Development (CLEUD) to formally confirm the work is lawful.
The 4-year rule is gone
Before 25 April 2024, there was a separate 4-year rule for building works and single-dwelling conversions. This has been abolished by the Levelling Up and Regeneration Act 2023. All planning breaches in England now have a single 10-year enforcement window. The old 4-year rule may still apply in transitional cases where the work was substantially completed before 25 April 2024 - but for anything done after that date, it's 10 years.
One critical exception: if the council can show that the development was deliberately concealed, the 10-year clock doesn't start until the date the council discovers the breach. Hiding work behind screens, fences, or other structures to avoid detection will not protect you.
If your retrospective application is refused, the council can issue an enforcement notice. This is a formal legal notice that requires you to either modify the development to make it acceptable, or remove it entirely and restore the site to its previous condition. You typically have a set period - often 3 to 6 months - to comply.
You can appeal an enforcement notice to the Planning Inspectorate. One of the grounds of appeal is that planning permission ought to be granted for the development - essentially a second chance at getting retrospective permission from an independent decision-maker.
Failing to comply with an enforcement notice is a criminal offence. This is where the legal consequences begin. The council can prosecute, and in serious cases the fines can be substantial. They can also carry out the remedial work themselves and charge you for it.
Many projects that homeowners believe needed planning permission were actually permitted development all along. Before submitting a retrospective application, check whether the work falls within the PD rules:
A rear extension within the depth, height, and boundary limits under Class A. A loft conversion within the volume limits under Class B. An outbuilding meeting the Class E conditions. If the work qualifies, you don't need retrospective planning permission - you need a Lawful Development Certificate (£274), which is a simpler process confirming the work is lawful.
This matters because a retrospective planning application is assessed against planning policy. If a neighbour objects, or the council has concerns about design or impact, they can refuse it. A Lawful Development Certificate is assessed purely against the PD rules - if the conditions are met, the council must grant it. There's no discretion.
This is increasingly common. You're buying a house and discover that a previous owner built an extension, converted the loft, or added an outbuilding without planning permission or a Lawful Development Certificate. The problem is now yours - you inherit any planning liability when you buy the property.
Your solicitor should check the planning history and flag any work that doesn't have documentation. If unauthorised work exists, you have options: ask the seller to apply for retrospective permission or an LDC before completion, negotiate a price reduction to cover the cost and risk of resolving it yourself, or take out indemnity insurance if the work is minor and has been in place for a long time without complaint.
For more on how previous work affects your remaining PD rights, see our previous extension guide.
Common mistakes that cost money
Assuming you need retrospective planning permission when the work is actually PD. Check the permitted development rules first. An LDC (£274) is simpler, faster, and cannot be refused if the conditions are met - unlike a planning application.
Relying on the 10-year rule without evidence. To prove immunity from enforcement, you need clear, time-stamped evidence that the work has existed continuously for 10 years - satellite images, dated photos, utility records. Without evidence, a CLEUD application will be refused.
Assuming building regulations approval means you have planning permission. These are completely separate systems. Having building regulations sign-off does not mean your work has planning permission, and vice versa.
Ignoring the problem when selling. A buyer's solicitor will ask about unauthorised work. Hoping nobody notices is not a strategy - it surfaces during conveyancing and can collapse a sale.
PD Assessment Tool
Before applying for retrospective planning permission, it's worth checking whether the work qualifies as permitted development. Our free eligibility check tells you whether your property type and location are eligible. If they are, the full assessment checks every relevant condition - so you know whether a Lawful Development Certificate might be the simpler route.
Free eligibility check. Full assessment £47.
Content verified against the Town and Country Planning Act 1990, sections 73A (retrospective applications), 171B (time limits), 172ZA (enforcement warning notices), and 174 (appeals). Time limit changes verified against the Levelling Up and Regeneration Act 2023 (effective 25 April 2024) and GOV.UK National Planning Practice Guidance on enforcement (updated 2024). Fee figures verified against MHCLG published schedule effective 1 April 2026. This page is for general information only and does not constitute legal advice.
April 2026