From GTPlanet Game Guides

London Street Circuit

London Street Circuit is a track for Gran Turismo 5: Prologue, with forward and reverse layouts.

As seen in the picture above (which is the forward layout), the track begins on Shaftesbury Avenue, then takes a Right turn onto Charing Cross Road, passing Lelcester Square, making a slight left and crossing over to St. Martin's Place, before taking another right turn past Trafalgar Square, continuing on Cockspur Street, turning right onto Haymarket, then left again onto Charles II Street, making another right turn onto Regent Street, passing the Picadilly Circus before going back to Shaftesbury Avenue to complete the lap.