In answer to Yorkie's post, I doubt that drivers usually sign beyond the limit of their depot's 'normal' work - though the WHL might be an exception, and it wouldn't surprise me if Fort William drivers signed the whole route into Glasgow, and indeed even had a booked job or two that far? The situation where drivers 'swap' trains is pretty rare though, and they'd usually be relieved at a location where there'd probably be a spare driver available - and would have at least a few minutes before picking up their next train.
One example, just out of interest, that I can think of - albeit on freight - is/was the Immingham to Jarrow tank train. I'm not sure whether the same driver works the return working, another train, or comes back on the cushions - he's booked to travel to Barnetby by taxi from Immingham, and relieve the driver who's brought the train over the short journey from Immingham. The reason? If he worked the train right through from Immingham, he'd go over his 'hours'.