I would highly recommend doing it around the topic of your intended course, even if its loosely related to politics. You have to remember that the top universities do not really care about your EPQ grade or the fact that you did it, unless it demonstrates your interest in the subject which could be really useful to talk about at the interview stage. I managed to get an A* last year, but I made the mistake of doing it about something completely unrelated to engineering/maths and so it won't really help me.