Thank you for the explanation Rgs and Chris, That possibility had crossed my mind but I thought they would surely not design that sort of operation on purpose, but they did, I imagine the grade was only slight and the risk of a run away was minnimised, but there must have been a few heart in mouth moments. I don't have that book (looks like I should have it) and have only seen a couple of photos with one or two coachs so I presume trains were very short, not much tail track to work with.
Wayne from Oz,