There is never any confusion, as Jerker says, by the drivers. The confusion arises in the minds of those not completely used to UK railway terminology. My local line is entirely single track with passing loops, yet still has an Up and Down direction. Even fen-tiger's "extended siding" to Wisbeach will still have Up and Down directions, even though it's a single line.  
In the area I'm modelling, there are 4 triangular junctions. Crossing one particular side of such a junction can mean an Up train suddenly becomes a Down train without changing direction!
				
			In the area I'm modelling, there are 4 triangular junctions. Crossing one particular side of such a junction can mean an Up train suddenly becomes a Down train without changing direction!
	