[G-CPTN]

Potted history:
The Routemaster double-deck bus was designed in the 1950s by London Transport, AEC (the engine and chassis maker) and PRV (Park Royal Vehicles, the body maker) to replace the AEC Regent RT type. Experimental vehicles took to the road in 1954, and full production began in 1959.
The bus used the AEC AV590 or Leyland O.600 diesel engine, an automatic gearbox by SCG (Self-Change Gears Ltd), power hydraulic brakes by Lockheed or Clayton Dewandre, and electrical equipment by CAV and Simms. A total of over 2700 were built in several variants, apart from the standard RM: the longer RML, coach versions RMC and RCL for the London Country operations, and the forward-entrance RMA for the London-to-Heathrow Airport shuttle service (a similar type being operated in Newcastle by Northern General Transport).
Heavy overhauls were carried out at Chiswick and Aldenham Works until these facilities closed. Surplus London Routemasters began to be sold in the 1980s, but in 1993 the remaining fleet was extensively refurbished, with new Cummins or IVECO engines, fluorescent lighting and other improvements. After the RM's 50th Anniversary celebrations in 2004 the number of Routemasters in service was reduced to just a handful, currently (2008) running on Route 9 and Route 15.

http://www.thermmanual.com/