Just a quick update. The Council were unable to help us duplicate the Mul-T lock keys for our flat (we were supposedly given a card allowing duplication when they changed the front door 13 years ago).
On recommendation from a Mayfair locksmith, we eventually had them duplicated at Brook Bros in Paddington. They do safes and are properly equipped for doing all kinds of duplications, even fob keys.
2 keys, 1 Fob for nearly £56.