I disagree with what most people are saying on here about Chemistry, I know it is a LOT of hard work, but in no means impossible, however make sure you know what exam board your college does, if its OCR B, I would ask you to think twice because the coursework is really really hectic and takes up about a month or two and since you'll be doing AS and A2 in a year, it will be hard and you will be juggling in terms of time management etc. That being said, most people end up retaking AS chemistry with their A2 anyway, and since you'll be studying AS and A2 together, it will be good because A2 helps with AS and vice versa. You'll be fine. If this is what you really want to do, then go for it! I'd suggest picking up a few chemistry books and biology books and just having a skim through them over summer before completely throwing your OFFER FROM UCL out the window. I hope it works out.