There was a documentary given away in a newspaper several years ago. Think it was either The Daily Mail or The Times. They might be able to help you.
But there has been a feature film called 'Buster' which starred Phil Collins as Buster Edwards who was involved. However, since the film was completed, Buster Edwards committed suicide. So the production does not have the tragic end.
The robbery is of some interest, as it took place on our local rail line. Although not in our county. Therefore near but so far away.