British planning has a famous front door — a full planning application — and a famous back door: permitted development, where the law has said yes in advance. What almost nobody mentions is the side door: a stripped-down process called prior approval, quietly responsible for thousands of extensions and tens of thousands of new homes every year.
A Narrower Kind of Check
Some permitted development rights come with a string attached: before using them, you must first ask the council whether its approval is needed for a handful of named matters.
That makes prior approval fundamentally narrower than a planning application — the council doesn’t get to reopen whether the development should happen at all, only the specific matters the legislation lists for that class.
The Larger Extension Process
The version most homeowners meet — the neighbour consultation scheme for extensions up to 6 metres on a semi, 8 metres detached.
Day 0 — the notification goes in
A written description of the extension, a simple plan, the addresses of adjoining properties, and the fee. The 42-day clock starts the day the council receives a valid package.
Days 1–21 — the neighbours get their say
The council writes to adjoining owners and occupiers, giving them 21 days to object. Silence ends the council’s role; an objection triggers an amenity-only assessment.
Day 42 — the clock protects you
If the council does not respond within 42 days, the prior-approval requirement is treated as satisfied and the owner may lawfully begin.
The little-known final duty
When the extension is finished, the owner must tell the council in writing, as soon as reasonably practicable, that it is complete.
If any adjoining neighbour objects, the council assesses only one thing: the effect on adjoining amenity — daylight, outlook, overbearing impact.
Planning a 6- or 8-metre extension of your own?
We prepare notifications that say exactly enough, answer neighbour objections with measured evidence, and keep the 42-day clock working for you rather than against you.
Prior Approval Beyond Extensions
The same side-door mechanism now carries some of the heaviest traffic in the planning system.
Commercial buildings to homes
Shops, offices, gyms and surgeries can convert to housing, with transport, contamination, flood risk, noise and natural light examined. A 56-day clock.
Agricultural buildings to dwellings
The countryside version lets barns become homes, with structural capability and location among the checked matters.
Building upwards
Additional storeys on certain existing buildings, with external appearance and impact on neighbours among the tests.
Demolition, telecoms and more
Knocking down a building, erecting communications masts and a long tail of other operations each carry their own prior approval regimes.
Eyeing a commercial or agricultural building for conversion?
We run feasibility on the prior approval routes before you commit a penny — qualifying checks, the matters the council will test, and the numbers that decide whether the deal stacks.
The Fixed List Cuts Both Ways
It cannot refuse for reasons outside the listed matters, demand documents beyond what the legislation specifies, or stretch the clock unilaterally. Equally, the discipline binds you — build even slightly beyond what the notification described and the deemed or granted approval doesn’t cover it.
Council gone quiet and the deadline has passed?
We confirm whether the council’s deadline has expired without a decision, put your right to proceed in writing, and deal with the council so you can start with certainty rather than hope.
Six Avoidable Mistakes
- 01 Starting work inside the 42 days because “the neighbours are fine with it”.
- 02 Describing the extension loosely, then building the tidied-up version.
- 03 Assuming a refusal is the end of the road.
- 04 Trying to use the larger-extension route on designated land, where it doesn’t run.
- 05 Forgetting the completion letter.
- 06 Confusing the council’s prior approval with sign-off of the construction itself.
Prior Approval FAQs
Select a question to reveal the answer.
Is prior approval the same as planning permission?
No — it's a condition attached to certain permitted development rights. The right to build already exists in national legislation; prior approval lets the council check a short list of named matters before you use it.
How long does prior approval take?
The council has 42 days for a larger home extension notification and 56 days for most change-of-use classes. Miss the deadline, and the prior-approval requirement is treated as satisfied.
Can my neighbours stop my larger extension?
An objection doesn't veto anything — it changes the process. The council must assess the effect on adjoining amenity, and many schemes are approved despite objections.
What can the council actually refuse prior approval for?
Only the matters the legislation names for that class of development — for larger extensions, the impact on adjoining amenity; for commercial conversions, transport, flooding, noise, contamination and natural light.
Do I need prior approval for a standard-size rear extension?
No. The notification process exists only for the enlarged depths; an extension within the standard limits proceeds without contacting the council at all.
What happens if the council refuses?
You can appeal, resubmit with changes, fall back to the standard-depth extension, or take the bigger scheme down the full application route instead.
What information do I have to submit?
A written description with depth, maximum height and eaves height, a plan showing it on the property, adjoining addresses, and the fee — nothing more.
Can I start building while the application is being considered?
No. Work may only begin once the council confirms approval isn’t required, grants prior approval, or lets the determination period expire without a decision.
Do office-to-residential conversions really avoid a planning application?
Many do, subject to floorspace and other qualifying limits, through the 56-day prior approval route, with the council confined to the listed matters.
Is the prior approval system the same in Wales?
No — Wales has not adopted several of the English prior approval regimes, including the larger home extension scheme, and its change-of-use rules differ significantly.
The Council Checks the List, and Nothing But the List
Prior approval is planning’s side door: a right already granted by legislation, paired with a short, fixed checklist the council may examine before you use it. For larger home extensions that means a neighbour window, a 42-day clock, an amenity-only test if anyone objects, and a completion letter at the end.
For conversions, the same mechanism runs on a 56-day clock with matters tailored to each class. Describe your scheme precisely, respect the clock, send the final letter, and the side door opens exactly as Parliament intended.