Smethurst's mother was from Stiffkey, and he was brought up in Sheringham, so his accent was very 'North Norfolk'. My adorable neighbours have the same way of speaking, totally different from the Norwich accent.
On Youtube, there's a recording of a monologue by him called 'The Great Train Robbery' (not a song) and the most fascinating thing about it is the way his voice rises an octave then drops down low, very typical of North Norfolk speech. It's delightful, and he sounds just like my neighbour's husband!