Normally front extensions, or those extending beyond a wall that forms the main (‘principal elevation’) entrance to a dwellinghouse would require planning permission. However, planning permission is not required for a porch over an existing door provided it is not more than 3 metres high, its external footprint does not exceed 3 sq. metres and the porch would be at least 2 metres away from any boundary of the house which borders a highway (including the pavement and verge).
See also Property Alteration Overview for more potential restrictions: https://planningaid.zendesk.com/hc/en-us/articles/203210341-Property-Alterations-Overview