The British Rail Class 103 diesel multiple units were built by Park Royal Vehicles with diesel engines by British United Traction (BUT). Ordered in the first half of 1955, 20 of these sets were built by Park Royal at the Crossley Motors works in Stockport of the ACV Group. They consisted of a power car and a driving trailer. Standard BUT equipment was fitted, with 'A' type engines.

A two-car set with 16 first class and 100 second class seats weighed just under 60 long tons, representing 1,150 lb (520 kg) a seat and had 5 hp per ton of empty weight or 4.35 hp per ton when full.