The Class 50 locomotives were built by English Electric between 1967 and 1968. Fifty examples were built, and were initially used to haul express passenger trains on the, then non-electrified, section of the West Coast Main Line between Crewe and Scotland. They were originally hired from English Electric Leasing, and were eventually purchased outright by BR around 1973.Class 50s were nicknamed "Hoovers" by rail enthusiasts because of the distinctive sound made by the air-filters originally fitted (these proved unreliable, and were removed during mid-life refurbishment, but the "Hoover" nickname stuck). Once the electrification of the line from Crewe to Glasgow was completed, the locomotives were moved to services in the south west of England, primarily on the mainline from London to Exeter, and were eventually retired from service in 1994 after being progressively replaced by the InterCity 125 High-Speed Trains (HSTs).