I believe it is possible to do a separate individual non UCAS personal statement for Durham, though I'd don't know if you can read zoology there, which overrides the UCAS one for Durham only if you choose to do it that way. But I may be wrong - worth a look though. Back before dinosaurs roamed the earth, when I applied to vet school, it was expected to only put down 3 vet school choices and have the other 2 for something like zoology, otherwise they would think you were being unrealistic! Now, of course, you will need to have a vet only PS as you say above.