The InterCity 125 (originally Inter-City 125) or High Speed Train (HST) is a diesel-powered high-speed passenger train built by British Rail Engineering Limited between 1975 and 1982. A total of 95 sets were produced, each comprising two Class 43 power cars, one at each end, and a rake of seven or eight Mark 3 coaches. The name is derived from its top operational speed of 125 mph (201 km/h). At times, the sets have been classified as British Rail Classes 253, 254 and 255.
British Rail (BR) initially developed the HST as an interim measure in the early 1970s, as delays and cost concerns began to threaten their primary high-speed train project, the Advanced Passenger Train (APT).