Hmm. I mean, not impossible, but.
There is one service area with a pub in it (near Beaconsfield). But it’s probably not that one.
Otherwise, well, every service area has a non-motorway access road, usually with gates and “no entry” signs and so on. And I suppose if Alice had her phone she could tell it “find the nearest pub”, and if she were lucky it would be less than an hour’s walk away. And then I suppose Brian could guess what she’d done and do the same thing. But it’s thin, devilish thin.