I hadn't associated being 'sent down' with the railway system. I had taken it as being sent down from a superior establishment rather than a physical movement. That's fun, I must try and chase it down - or do you already have a reference?

I don't associate "sent down" with the railway system either - sorry if I gave a misleading impression. My intention was to give examples of another convention of "up" and "down" beyond those that had already been mentioned.