Oscar winner Jim Broadbent will play the detective charged with tracking down the Great Train Robbers in the second of two programmes dramatising the historic heist.
The actor, who won an Oscar in 2001 for his performance in Iris, will play Tommy Butler in the BBC's The Great Train Robbery: A Copper's Tale.
Other members of the cast include Robert Glenister, Tim Pigott-Smith and James Fox.
Broadbent said: "I'm thrilled to be part the Great Train Robbery film.
"I have such strong memories of the massive impact of the actual robbery and it is wonderful to find out from the script so much of the real story.
"Tommy Butler is a fascinating copper of the old school and I anticipate great fun playing him."
Executive producer and writer Chris Chibnall, whose hits include the recent ITV success Broadchurch, said: "I've enviously watched Jim's work on other writers' scripts for years and I have to keep pinching myself that he'll be bringing Tommy Butler to life in A Copper's Tale.
"It's a dream piece of casting, leading an ensemble of thoroughbred great British actors."
The first episode, A Robber's Tale, begins with an earlier robbery at Heathrow Airport in 1962 and shows how the train heist was planned, rehearsed and executed, from the perspective of Bruce Reynolds, who died this year at the age of 81.
Reynolds will be played by Hollywood star Luke Evans.
The films come months after ITV screened a drama series, Mrs Biggs, based on the aftermath of the robbery and looking at life on the run for Charmian Biggs - wife of Ronnie.
The gang targeted a mail train from Glasgow in August 1963 and escaped with a then record haul of £2.6 million after they pounced in Buckinghamshire.
The train driver Jack Mills was struck with an iron bar and never worked again, and it has never been established who delivered the blow. He died in 1970.