400i Head gasket blown?

Anyone who has tried to remove a 400 cylinder head, (engine in car) will know the feeling of triumph as it starts to rise! If you ever need to do this yourself take some valium first, and warn your family to give you a wide berth!
Anyway the head is now sitting on the bench. The leak was from number 6 cylinder and visually the combustion chamber looks sound, as does the liner.
I want to have the head cleaned up/skimmed if needed, and crack tested. Does anyone know a good machine shop in London or Essex where I could take the head for checking?