The standard BBC4 should be aiming for is the pair of BR documentaries that Channel 4's 'Equinox' program produced in the late 1980s and early 1990s.
'Running to Time' which charts the development of the Class 91 'Electra' locomotive is just sublime (and by god does it give plenty of juicy material to discuss in the British Rail thread running in this sub-forum).
https://www.youtube.com/watch?v=VvsIYaRmRAM
'Trouble on the Line' is another, a more general program about British Rail crumbling and about to collapse. Roger Ford takes a starring role, as do a couple of other experts - Richard Hope and Mike Smith.
https://www.youtube.com/watch?v=WJfaKKVS5Hc
I know such documentaries are now deeply unfashionable, but these were documentaries which everybody from school kids through to BR drivers, guards and managers learned from.