Miller began his career with the London & North Eastern Railway (LNER) as an apprentice, working under Sir Nigel Gresley.

[1] By the 1960s, when BR was withdrawing steam locomotives and dismantling facilities for them, Miller was one of several people who provided support to Alan Pegler in his attempts to run the preserved Flying Scotsman.

It was in this position that Miller was credited with instigating the development of the InterCity 125, known as the High Speed Train (HST).

As a stop-gap measure, engineers devised plans for a 125-mile-per-hour (200 km/h) "High Speed Diesel Train", which Miller submitted to the British Railways Board (BRB) at the beginning of 1969; the submission won the endorsement of Henry Johnson, chairman of BRB.

[8] The project returned the remaining prototype HST power car, number 41001, back to working order at Neville Hill TMD in 2014 after years of static display in the National Railway Museum in York.