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 alterations and permitted development for more potential restrictions.