This is the only Grand Theft Auto game set in a real city.
An add-on pack for this game, Grand Theft Auto: London, 1961 (1999), was released a month afterwards. It used the same map but featured 8 new missions and 19 new vehicles (which replace some of the vehicles from the first game) and also a multiplayer deathmatch area loosely based on the city of Manchester. This game was only available for the PC as downloadable freeware.
This game has a little known add on called Grand Theft Auto: London, 1961 (1999), it was a free download that required this game (and so the original Grand Theft Auto (1997)) to play and was only available on PC, it was not well known because of its inconspicuous download location and lack of publicity. It is available from the Rockstar site for free (as of 2006).