The British Rail Class 50 is a class of diesel locomotives designed to haul express passenger trains at 100 mph (160 km/h). Built by English Electric at the Vulcan Foundry in Newton-le-Willows between 1967 and 1968, the Class 50s were initially on a 10-year lease from English Electric Leasing, and were employed hauling express passenger trains on the then non-electrified section of the West Coast Main Line between Crewe and Scotland. Initially numbered D400–D449 and known as English Electric Type 4s, the locomotives were purchased outright by British Rail (BR) at the end of the lease and became Class 50 in the TOPS renumbering of 1973.

The English Electric Company Limited (EE) was a British industrial manufacturer formed after the armistice ending the fighting of World War I by amalgamating five businesses which, during the war, had been making munitions, armaments and aeroplanes.