[1] Earlier internal studies by British Rail Research in the early 1980s had focussed on the feasibility of developing a 25.5 m long InterCity coach to succeed the Mark 3 and evaluated the technologies needed to reduce the capital and operating costs by 30%.

Indeed, during 1987 British Rail had considered increasing the length of the Mark 4 to 25.5 m (with 18.13 m bogie centres[3]) but the in-service date of 1989 and complexity of changing the design to suit caused the variation order to be shelved.

In early 1991, tenders were called for up to 45 ten carriage sets with GEC Alsthom, Bombardier/Prorail, and British Rail Engineering Limited/ABB invited to bid.

After the InterCity 250 project was scrapped, Virgin Trains, who operated the InterCity West Coast franchise from the privatisation of British Rail until 2019, commissioned new rolling stock in the form of Class 390 electric multiple units, rather than the Class 93 locomotive and separate Mark 5 carriages proposed by British Rail.

These will be initially used on services between Liverpool and Newcastle from 2018, before being transferred to other routes upon the delivery to TPE of its fleet of Class 802 bi-mode multiple units.