No, you don't have to read a lot in preparation for it ... or at least not any more than you're already doing for interviews (and I remember refering to something that happened in work experience). There's no set thing you're expected to say in answer to any question, just a general awareness of medically related issues and/or a logically thought out arguement, whatever conclusion you reach. The questions are quite structured. I would read the official BMAT book - that has a very good chapter on section three.