Identify the exact application first
“Prior approval” is not a single permission with one universal deadline. Different classes have their own procedures and consequences for non-determination. Find the part and class on the application, together with the submitted drawings, required information and evidence of receipt. [2][4]
The relevant date is the one produced by that procedure, not a date inferred from when a drawing was first emailed, when neighbours stopped commenting or when a builder was booked. Establish the applicable period from the actual submission record before relying on it. [1][3]
Larger home extensions: a conditional 42-day route
For the Part 1 Class A larger home-extension procedure, development may be able to proceed where the prescribed period expires without the council notifying the applicant of its determination. The Planning Portal guidance describes the 42-day outcome alongside written confirmation that prior approval is unnecessary and written approval where required. [1]
This does not make an otherwise ineligible extension lawful. The right's limitations and conditions must still be satisfied, including the correct notification procedure and information. A proposal exceeding an applicable height or depth limit is not rescued by administrative silence. [5][6]
Before relying on expiry, check what the council received, when it received the required material, and whether a decision was notified. Keep the actual correspondence rather than relying only on a planning-register status label. Where the facts or calculation are disputed, resolve the lawfulness question before committing to construction. [1][7]
Upward extensions: eight weeks is not automatic approval
For additional storeys under Part 1 Class AA, government guidance states an 8-week determination period. The legislation nevertheless prohibits beginning before receipt of the council's written prior approval. The government's stated remedy for non-determination is an appeal. [2][3]
This is a particularly important distinction where an upward-extension project is being compared with a neighbour's larger rear extension. The two projects can both be permitted development and both need prior approval, yet have different legal consequences when the council is late.
A certificate or ordinary application is different again
A Lawful Development Certificate application is not granted because its decision period expires. The Planning Portal explains that failure to determine within 8 weeks can give rise to an appeal. A certificate still needs a positive determination; the passage of time alone is not the document. [8][9]
Likewise, the normal target for a householder planning application is not a permission to build on the next day. Government guidance provides appeal routes for non-determination rather than a general rule of permission through silence. [10][2]
Keep the evidence tied to the design
Any lawful route established by the application concerns the relevant described development and details. Do not treat expiry of a period as permission for an amended project which was never submitted or which fails the class limits. [1][3]
For a disputed start date or deemed outcome, obtain a project-specific assessment of the procedural record. Starting first and trying to establish the legal basis later can leave the central planning question unresolved. [7]