In reply to winhill: We have a statutory requirement for site notices if the development:
- Affects a Conservation Area
- Affects a Listed Building
- Is a major development
- Affects a PROW
- Is accompanied by an Environmental Statement
- Is a departure from the Unitary Development Plan (or other adopted local plans)
These are all displayed by the local authority. We also generally put one up ourselves when there are no close neighbours but passers-by (walkers for example) may have an interest.
For a straightforward change of use I would send one out to the applicant and ask them to display it for 21 days and then fill in a form telling me they have done so. Many do, but it actually isn't a statutory obligation. For a household extension no site notice is needed (unless of course one of the above reasons applies).