I've got myself all flustered ... tell me if I've got this right.
Case 1 Mainline
--------------- 'Up' -> trains to London 'Down' -> trains from London
Case 2 Branch
------------- 'Up' -> trains to the junction with the main line 'Down' -> trains along the branch from the junction
Case 3 'Mainline' built before there was a connection to London
--------------------------------------------------------------- 'Up' -> Trains to BigTown (or town where Rly Co has it's Offices/depots) 'Down' -> Trains from BigTown as above
Which assuming I'm correct above what happens with branches/lines that are essentially circular?
And taking 'case 3' above what happens when BigTown railway finally gets a connection to London and it turns out that the existing 'up' and 'down' lines are pointing the wrong way?