For me, it's the little things--like lanes that suddenly turn into "turn only" lanes, and how sometimes the signs come *right* before you need to turn (and maybe get over in a hurry!) that would definitely foul up that part of the test. I get lost ON MY OWN heading for the city centre (which, in Manchester, is quite an accomplishment) because roads bend in odd directions and signage is not always clear (to me). It's a lot better now that I have experience, but I think that, nervous as I was on the day of the test, that could really have messed me up!
I'm sure the driving instructors will incorporate it into the lessons though!