There is a company in Wymondham that does a lot of hot rod stuff - they get to the shows but I can't remember their name, something like Autopower, maybe? Carl Powles is up near Hull, but I don't know if does this stuff full time? Or look through the trader section on here?
I think others would agree that whoever you go to, make sure you have seen some of their paid work (not just one of their mates' cars), and do a good search on their name to be sure they don't have a shady past. There are far too many stories on here of folks who have paid lots of money out and got very little in return.