Bridget Jones's Diary

Plot hole: In the first chapter, when Bridget is going to Grafton Underwood for the Turkey Curry Buffet it's is clear that she drove there - she mentions getting onto the M6 by mistake and jamming her foot down on the accelerator - but towards the end of the buffet, Mark is made to offer her a lift back to London, to which she replies that she will be getting the train back in the morning. Surely she would just drive back? What would be the point in leaving her car at her parents' house?