You can't split them up into battalions, etc. (here's hoping you can in WITP), but you can transport part of a unit and leave the rest. The problem with this is that you don't get an even split in terms of combat and support troops, artillery, etc.
While the battles the British fight may differ in the widest possible ways, they invariably have two common characteristics – they are always fought uphill and always at the junction of two or more map sheets.