On Sep 29, 12:16*am, "Richard J." wrote:
wrote on 28 September 2010 08:13:05 ...

There's also the problem of deciding where in central London the
southbound line say would change from being 'up' (which is normally
but not always TO London) to 'down' - away from London.

Where does the up/down orientation change on Thameslink in central London?

Up and Down swap at the former Farringdon Junction, where the line to
Moorgate used to diverge. Services from the north to Moorgate ran Up
all the way, services to Blackfriars still change designation to Down
at the site of the junction.