As Lwescott has said, I would recommend getting some work experience. Not only will this allow you to know for certain that it's what you want to do, it's also a requirement for entry onto veterinary courses. Vet schools want to admit people that they know have explored the profession and have a good idea of what to expect. Requirements vary but are highest at Liverpool, who want ten weeks' worth. I'd suggest having a read of the Big and Shiny Work Experience Bible.
As far as getting onto the course goes, Nottingham offer a foundation year course for people who didn't do the right subject combination, but since all vet schools interview it's too late to apply for this year, vet places don't go into clearing, and they wouldn't accept a transfer from a bio degree. Your best option in my opinion would therefore be to take a year out and apply in your gap year (or a year later, if you're worried about getting enough work experience). In this year you could also do A2 chemistry to open your options up and allow you to apply to other vet schools (I know Notts is your fave, but it's competitive to get in so it might be worth increasing the number of places you apply to).