Definition of "XC"

As the 1857 to Manchester Piccadilly rolls in, I scan the windows and realise there are plenty of spare seats, so I hop aboard. The train is a '221'+'220' combo to allow for social distancing - a luxury on an XC train as normally you're playing sardines, so I make the most of it.

2020 December 2, Paul Bigland, “My weirdest and wackiest Rover yet”, in Rail, page 68