Early on, a plot hole about Tom's bus pass appears: he won't be able to use his Scottish pass in England (and it's the same vice-versa).
But this is woven into the story later on.
As others have said, Timothy Spall's performance is spellbinding. OK, a little too much PC (is half the population of Land's End really black?), but that's almost obligatory these days and the film does succeed despite it.