hey - same here ^^ I was interviewed two years ago. They're really lovely people and will do their best to put you at ease. I would strongly suggest that you really do your research about Keele and pbl and think about why you applied there and why you think pbl especially suits you - I know you've already done this, but sometimes it's difficult to express it unless you've prepared. They will obviously ask you why medicine and they asked me quite alot about my work experience and what I learned from it. They gave me a scenario to discuss (in connection with the internet and health information being more readily available). Other interview questions don't really vary that much from place to place, so I would look at the type of questions other universities have been asking and think about what your responses would be - I actually wrote down some of my answers when preparing, because I think it helps to clarify things in your mind (although it may seem slightly obsessive at the time!). Other than general questions, just concentrate on Keele and pbl - I think it would be really helpful to talk to students who are actually on the course and get a better idea of the benefits of studying at Keele. It will also show that you've really done your homework and made your choices wisely.
best of luck!
x