I'm not in veterinary medicine but I do know that it is an extremely competitive course and that Universities are very specific in what they ask for at A Level.
To be honest, I'm not sure you would be able to apply for that course with those three A Level subjects. I see that Cambridge asks for Chemistry, and at least one of Biology, Physics or Mathematics - it doesn't accept Psychology. You would be well advised to follow that template if you wanted to be a vet.
Whichever of the degrees you eventually opted for, I would still advise against Criminology and probably Psychology too.
Which are your best subjects at GCSE?
Ultimately, what you need is a combination of suitable subjects and good grades.
PS When you choose your degree subject, I would think carefully about how many doors it will open re employment after you graduate. Don't choose a subject which has 'limited currency' like Criminology.