Under the chairmanship of Stanley Raymond, it was decided to reduce journey times further on long-distance trains by increasing line speed to 125 mph where practical - the maximum considered possible on Britain's Victorian-age railway.
The rapid development required for the HST in 1969 made the Mark 3 coach design the obvious choice for this train, and in 1972 the first Mark 3 coaches were built, ten for the prototype HST [REF].