Published by Giovanni Patania
on 01/03/2026
There has been an unauthorised development on your property for years. It might be a rear extension, garage conversion, or outbuilding. So far, the council hasn’t taken enforcement action. The 10-year rule in planning might give you the chance to make it legal without applying for planning permission.
In this article, find out what the 10 year rule is and how it works. Also, discover how you can become immune enforcement action by your local planning authority.
What is the 10 year rule?
The legislation we’re covering in this article is Section 171B of the Town and Country Planning Act 1990.
This rule sets the relevant time limit for taking enforcement action against breaches of planning control. After that time has passed, a development becomes lawful. You don’t need to obtain planning permission.
The Levelling-up and Regeneration Act 2023 changed everything in England. From 25 April 2024, all breaches are now subject to a 10 year enforcement period. Before this, the time period was four years, however, there are certain circumstances that may alter this timeframe.
The current situation for property owners is:
- Developments substantially completed before 25 April 2024: May still qualify under the old 4 year rule.
- All unauthorised developments from 25 April 2024 onwards: 10 years before you get immunity
Which developments qualify under the ten year rule
Below, find out which unauthorised developments may become lawful under the ten year period.
Operational Development Requirements
Operational development means when physical building works are in progress. The clock starts ticking for immunity from enforcement action at the point of substantial completion.
Substantial completion is when a development reaches the point you can use it for its intended purposes. That’s even if minor finishing touches remain.
Common operational development types include:
| Activity | Type of Planning Breach |
| Extensions and additions | Rear, side or front extensions that go beyond permitted development limits for size, height, or proximity to boundaries. |
| Outbuildings | Garages, conservatories, garden rooms or other detached structures. Built without the necessary planning permission. |
| Boundary works | New or altered walls, fences or gates that exceed height restrictions or breach local council regulations. |
| Conversions | Loft or basement conversions that change the building’s external appearance beyond what PD allows. |
| Agricultural land structures | Barns, storage buildings or dwellings erected on agricultural land without formal planning approval. |
Changes of use subject to the ten year period
Changes of use, like the following, have always required 10 years grace, stretching back before the 2024 changes.
| Type of development or use | What the rule covers |
| Houses in Multiple Occupation (HMOs) | Changing a single home (Use Class C3) into an HMO (Use Class C4 or sui generis) without planning permission. |
| Commercial to residential conversions | Turning shops, offices or industrial premises into HMOs and homes. This is without formal permission or permitted development rights. |
| Mixed-use or commercial-to-commercial changes | Altering a property between different types of business use. Or combining residential and commercial elements without consent. |
Applying for your lawful development certificate
You can remove any risk of potential formal enforcement action by applying for a certificate of lawfulness. Here’s how:
Evidence requirements for a certificate of lawfulness
You need to provide clear and convincing evidence on the balance of probability that your development meets the requirements. This evidence must be up to the standard set in the National Planning Policy Framework.
In other words, the local authority needs hard proof that;
- The alleged breach happened over ten years ago
- The existing use has been continuous (like operating as an HMO).
If you don’t provide enough evidence, they can refuse the certificate. You can reapply with further documentation. The table below shows the type of evidence a planning enforcement team would expect:
| Supporting evidence | Examples | Purpose |
| Occupancy proof | Utility bills, council tax records, and electoral register, tenancy agreements, vehicle registration documents | Prove continuous use over the time limit |
| Physical evidence | Dated photographs, satellite images, building regulations records | Prove substantial completion and age |
| Legal document | Tenancy agreements, statutory declarations, vehicle registration documents | Provide convincing evidence of timeline |
If you lack evidence, then get statements from previous owners, neighbours or tenants. Their testimony as they carry weight in the process. The more witnesses, the better.
For operational development cases, aerial photography is powerful as is historic satellite imagery.
The application process and timelines
Submit your application to the local planning authority. You can download a lawful development certificate application from their website or Planning Portal. There is a charge for making an application which varies between councils.
Once you’ve sent your evidence in, the council has eight weeks to respond, unless you agree to extend. They grant permission based on the evidence, not on planning merits. In other words, the scrutiny is a lot less than current proposed developments that require planning permission.
If your application is refused, you can appeal to the Planning Inspectorate. Such a notice of appeal must follow the specific procedures set out by the council.
HMO Architects note: You can apply for retrospective planning permission. However, this is risky as it will put your older property development project through the modern formal planning permission process. Planning laws tighten over the time, meaning your extension or conversion could now fail. Try the lawful development certificate route before going for retrospective planning consent.
Exceptions, enforcement notices and professional guidance
There are certain circumstances where the ten year rule doesn’t apply. They include:
- Deliberately concealed developments: Hiding a development project from the authorities.
- Listed buildings: No time limits apply to unauthorised works on protected buildings.
- Conservation areas: Demolition in conservation areas remains subject to enforcement regardless of time.
- Outstanding natural beauty: Special protections may extend enforcement powers in designated areas.
HMO Architects: planning law specialist architects
HMO Architects has a 97% success rate in planning matters. On behalf of our clients, our planning permission experts have worked with 200 councils to make sure our clients’ projects meet both national and local standards.
Planning legislation is complicated. Protect your property and development by working with one of our planning consultants. They’ll review your situation, advise on the best route, and prepare the paperwork to give you the strongest chance of approval.
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Published by Giovanni Patania
on 01/03/2026
Giovanni is a highly accomplished architect hailing from Siena, Italy. With an impressive career spanning multiple countries, he has gained extensive experience as a Lead Architect at Foster + Partners, where he worked on a number of iconic Apple stores, including the prestigious Champs-Élysées flagship Apple store in Paris. As the co-founder and principal architect of WindsorPatania Architects, Giovanni has leveraged his extensive experience to spearhead a range of innovative projects.
