Prior Approval London 2026: Complete Guide
When you need prior approval, how to apply, and what the council considers. A middle ground between permitted development and full planning permission.
TL;DR - The Quick Answer
Prior approval is a streamlined council notification process sitting between permitted development and full planning permission. For householders, it is most commonly required for single-storey rear extensions exceeding standard limits: up to 8m on detached houses and up to 6m on semi-detached and terraced properties. The application fee is £120, neighbours have 21 days to comment, and councils must decide within 42 days. If no decision is issued, approval is automatically deemed granted. Conservation areas, listed buildings, and Article 4 areas are excluded.
Prior approval is a streamlined planning process for specific types of development that are technically "permitted development" but require council notification. The council can only consider limited matters-typically neighbour impact, transport, or flooding-not the broader planning merits.
When Prior Approval Is Required
Larger Home Extensions
Single storey rear extensions between 4-8m (detached) or 3-6m (other houses). This extends standard PD limits but requires neighbour notification.
Office to Residential (Class MA)
Converting offices to homes. Council considers transport, flooding, contamination, and impact on provision of office space.
Agricultural Buildings
Converting agricultural buildings to residential. Siting, design, transport, flooding, contamination, and noise considered.
Telecommunications
Mobile phone masts and equipment. Siting and appearance are the main considerations.
Larger Home Extension Rules
The most common householder use of prior approval is for larger single storey rear extensions that exceed standard permitted development limits.
| House Type | Standard PD | With Prior Approval |
|---|---|---|
| Detached house | Up to 4m | Up to 8m |
| Semi-detached | Up to 3m | Up to 6m |
| Terraced house | Up to 3m | Up to 6m |
Note: Maximum height 4m, eaves 3m. Must be single storey only. Does not apply in conservation areas, AONB, or to listed buildings.
| House Type | Standard PD Limit | With Prior Approval | Fee |
|---|---|---|---|
| Detached house | Up to 4m | Up to 8m | £120 |
| Semi-detached | Up to 3m | Up to 6m | £120 |
| Terraced house | Up to 3m | Up to 6m | £120 |
Source: Mayfair Studio project data • Data as of 2026
The Prior Approval Process
Submit Application
Complete form, pay £120 fee, provide site plan and elevations showing proposed extension.
Neighbour Notification
Council writes to adjoining neighbours giving 21 days to comment on impact.
Council Assessment
Council can only consider impact on amenity of adjoining properties-not design, materials, or planning policy.
Decision (42 Days)
Three outcomes: prior approval granted, prior approval refused, or prior approval not required. No response = deemed approval.
What Council Can and Cannot Consider
Can Consider
- Impact on adjoining neighbours' amenity
- Loss of light to neighbours
- Overbearing impact
- Overlooking (if relevant)
Cannot Consider
- Design quality or materials
- Whether it suits the area
- Planning policy preferences
- Impact on your own amenity
Prior approval for a larger home extension costs £120 and takes a maximum of 42 days to determine. It allows single-storey rear extensions up to 8m on detached houses and up to 6m on semi-detached and terraced properties - beyond standard permitted development limits. If the council does not respond within 42 days, approval is automatically granted. Conservation areas and listed buildings are excluded.
Frequently Asked Questions
Can neighbours stop my extension?
Only if their objection relates to impact on their amenity and the council agrees the impact is significant. General objections about not liking the development are not valid grounds for refusal.
What if the council doesn't respond?
After 42 days without a decision, prior approval is deemed granted. You can proceed with development, though it's wise to get written confirmation.
Can I appeal a refusal?
Yes, you can appeal to the Planning Inspectorate. Appeals are free and typically decided within 8-12 weeks for householder applications.