And there you have one of the problems with slip coaches: you can't just catapult them on to the back of a passing express. They had to be worked back, often as through coaches, to their starting point, although there were some cases where the coach formed a return through working: there were a number that were dropped off Up workings at Reading, for example. There was, until the final years, also the problem that through coaches did not have gangways, so if formed in an express the passengers couldn't get to the Restaurant Car. This all added to the difficulties of using the coaches and made them, even in an era of low stock utilisation, a poor bargain.
I refer the honourable Member to the Pigeon Rail Systems instantiation of the pils coach: http://www.railforums.co.uk/threads...un-which-would-you-choose.166085/post-3524955
Adrian Vaughan gives a description of the up slip at Reading in "Signalman's Morning".
