I can’t speak personally about the interview as I must admit I’ve never had one, or even applied for this programme. However, I do know that with graduate programmes, your qualifications are very important, so make sure you let them know how good your qualifications are!
To anyone thinking about this who hasn’t completed their exams yet until the summer, then all I can say is work very hard! Getting good grades sets you above the rest, which is what graduate programmes are looking for these days.