The BBC’s film of The Great Train Robbery 50 years on scores not only on the pace of drama (from the creator of Broadchurch), but on the loving attention to detail – unlike most TV recreations of period railways. The cab of the Class 40 locomotive, which was a top-link express loco of the Beeching era, was full of vintage English Electric charm. but would the exterior have been so shiny, when diesels lived cheek-by-jowl with filthy steam locos?