In the early 1970s the BRB were faced with a position that within around 10 years the majority of their main-line diesel traction would need replacement. Financial limitations were tight and the possibility of mass electrification was not possible, therefore a new generation of high-speed diesel train had to be developed. This culminated in the production of a 'Prototype' high-speed set originally classified as locomotive and stock. The locos or power cars were Class 41, (later 252). After seeing the advantages of this design, production orders were placed for like trains for operation on the Western, Eastern, Scottish and London Midland Regions.
The prototype set was developed at the Railway Technical Centre, Derby, with the power cars being constructed by BREL Crewe Works in 1972. The passenger cars being constructed by BREL at Derby Litchurch Lane Works. The power cars or locos as they were initially known had a main driver's position at one end which was aerodynamically shaped, the other, flat end, had an auxiliary driving position for shunting purposes. The two power cars which were of light-weight construction were built in early 1972, emerging in June and August. As soon as suitable stock was available trial running commenced, first on the
Eastern Region and latterly on the Western Regions.
The power-unit used in these vehicles was a Paxman 'Valenta' 12RP200L developing 2,500hp, electrical equipment was supplied by Brush.
Upon introduction the two power cars were numbered 41001 and 41002. After a short period the entire 'set' including the passenger coaches became unit Class 252, at the same time the power cars were renumbered 43000 and 43001. After operating its initial proving trials on the Eastern Region the prototype High Speed Diesel Train (HSDT) was transferred to the Western Region where it was deployed on Paddington Bristol/Weston-super-Mare services. Following the introduction of production HST sets the prototype unit was withdrawn, the power cars passing to the Research Division at Derby, and used to power various high speed development trains.
After restoration, one of the historic prototype power cars has become a resident in the National Railway Museum (NRM) at York, while the other was sadly broken up for scrap. Most of the prototype passenger coaches were later converted into production HST cars, but some saw departmental use.
The prototype HST was painted in grey 'reverse Pullman' livery with a broad blue band on the upper part of the body and full yellow ends were applied.