If he is in london he can just go home then go to gatwick for the exams.
Its what i did as a flight home and then back was cheaper than bnb for 10 days.
Gatwick also tends to always have free slots where as the other centers can run out and the likes of oxford book months in advance so as a distance learner you have no chance of getting a place there so more than likely have to position to gatwick anyway.