Class 253 and Class 254 were the classifications allocated to the production High Speed Train units. The former class was used for Western Region sets, operating out of London Paddington, and the latter for Eastern Region sets, operating out of London King's Cross, since these regions used different formations.

History

When originally built, from 1976, the High Speed Train (HST) units were considered to be Diesel Electric Multiple Units, with semi-fixed formations of power cars and intermediate passenger-carrying trailer cars. They were all numbered in the carriage series, in the 4xxxx series set aside for HST and Advanced Passenger Train vehicles. Numbers followed those allocated to the prototype Class 252 unit, so for instance, power cars were numbered from 43002 upwards.

This situation changed in the 1980s, since when the power cars have been considered to be locomotives, known as class 43, and the trailer cars as hauled Mark 3 carriages. Despite this change in designation, no power car or carriage was renumbered.

In 2000, Class 255 was allocated for the reformation of certain HST power cars and trailers into semi-fixed formation trains, to be known as Virgin Challenger units, for use by Virgin Trains after the introduction of their new 'Voyager' trains (Classes 220 and 221). These formations would have involved power cars sandwiching one Trailer First, a Trailer Buffet, two Trailer Seconds and a Trailer Guard Second. However, these plans came to naught due to escalating costs within the British railway industry.

Formation

The vehicle types used to form High Speed Trains are listed below: