The Class 40 locomotives, built by English Electric between 1958-1962 and eventually numbering 200, were once the pride of the British Rail (BR) early diesel fleet. They were amongst some of the first diesels built for BR as part of their modernisation programme to rid the UK of steam locomotives. Despite their initial success, by the time the last examples were entering service they were already being replaced on some top-link duties by more powerful locomotives. As they were slowly relegated from express passenger uses, the type found work on secondary passenger and freight services where they worked for many years, the final locomotives being retired from regular service in 1985. Seven examples remain in existence.
The Class 50 locomotives, built by English Electric between 1967-1968 and eventually numbering 50, were the last purpose-designed mixed-traffic locomotive built in the UK. Upon their introduction they were used on the West Coast Main Line (WCML). The aim was to speed-up passenger timings on the then non-electrified portion up to Glasgow. By 1974, the entire line had been electrified so the locomotives were re-deployed to other regions as had been planned. The introduction of High Speed Trains (HSTs) on Western Region services saw the class transferred to other duties. By 1984, sufficient Class 50s were available for them to become the locomotive of choice on the Southern Region Waterloo-Exeter route and here they largely remained until being retired from regular service in 1992. Eighteen examples remain in existence.
The Class 55 (Deltic) locomotives, built by English Electric between 1961-1962 and eventually numbering just 22, were perhaps the most iconic diesel locomotives ever to run on the national network. They were designed for high-speed express passenger services on the East Coast Main Line (ECML) between London King's Cross and Edinburgh. They gained the name ‘Deltic’ from the prototype locomotive which in turn was named after its twin Napier Deltic power units. At the time they were built they were the most powerful single-unit diesel locomotives in the world and transformed services on the line until their withdrawal in 1982. Six examples remain in existence.