Do you have to tell neighbours about planning permission?

Publicity for a planning application is a statutory duty on the local planning authority, not the applicant. Once your application is valid, the council writes to adjoining occupiers and/or posts a site notice, opening the 21-day consultation. You don't send anything to the neighbours yourself.

That said, telling them anyway is one of the cheapest pieces of planning insurance available. Neighbours who first learn of an extension from a council letter are measurably more inclined to object than ones who saw the plans over a cup of tea and had their questions answered.

The Party Wall etc. Act 1996 is a different regime with a genuine personal duty: if you're cutting into a shared wall, building astride or up to the boundary, or excavating within 3 metres (sometimes 6) of a neighbouring structure, you must serve formal notice — typically one or two months before the work starts.

Party wall consent is separate from planning permission. You can hold full planning approval and still be unable to lawfully start until the party wall process is resolved, by agreement or through surveyors.

For permitted development projects there's usually no neighbour notification at all — with the exception of the larger home extension route, where the council consults adjoining owners as part of prior approval.