I think you should apply for the 5 year course. The standard Nottingham offer is AAB (As in Biology and Chemistry) so it doesn't matter if you slip up a bit on your third subject. Also, Nottingham seem to be much less strict on grades in general and more focused on you as a person then other vet schools. I was offered AAB, but I ended up getting A*BB at A level, but they still let me in even with a B in Chemistry. Also, I know some people on the course currently who got BBB at A level and still got in. So if you do really well at interview and all the other stages, you could still get let in even with not very good grades.