What kind of work experience have you done for vet? Have you been able to get a variety of placements both in vet clinics and on farms, in kennels, etc? How did you enjoy those?
Ditto for design. Have you been able to get any work experience in the field as yet?
Vet is an academically hard course. What grades did you miss? And did you not quite meet them after resitting? Are there any particular reasons/special circumstances/etc. for that? Don't get me wrong, lots of people don't get the grades first or even second time and go the graduate/other routes. Having said that, if you struggled with say biology at A level, I would be slightly more concerned about you struggling with the academic requirements for the vet course.
Are you talking about going the grad route for vet then (doing biovet science then applying to vet)? Are you aware of what this entails? There is virtually no financial support for a grad vet student, so you are looking at tuition fees of 9,000GBP to over 28,000 GBP per year, not including equipment and costs of living. This is for a degree which in your first few years you might only earn mid-20,000 GBP salary, out of which you need to pay the bills, support yourself, and start paying back your loans. Even a mid-career vet does not earn as much as other "comparable" degrees eg human doctors, lawyers, dentists etc. I did the grad route and learned a lot and I think I benefited from being a little more mature and having the prior knowledge I had from my degrees, so if you can afford it and it is what you want by all means do it. Just trying to be honest.
Both degrees are as I understand it very competitive. How do you feel about that?
Design you may be able to set your own hours etc. a bit more. Vet your hours will likely be set by the clinic you work for and/or the needs of the clients.
I can't think of much else. Is there a design forum you could post in, to get their feedback as well?
Good luck!