Hi there
As kookaburra said, really isn't much that we can say about the interviews, there is a little bit of advice on the website which you can look up (it's under the 'Admissions Process' section), but apart from that, try not to worry - they're not designed to catch you out or anything, they just want to see what you're like in practical and team working situations - so it kind of defeats the point if you have an idea of what to expect! Just be yourself, there's really not any kind of preparation you can do, otherwise they'd have given you advice on it. Good luck!
PS have you thought about going back to do the chemistry a level to widen your options?