Just figured I would add my thoughts to what everyone else has said.
I was in a similar-ish position to you, didn't get the grades at a level, so I panicked and got an offer through clearing for animal science. Realise in my first year that I wasn't happy with this and still wanted to go down the vet route, but didn't want to waste the years time and money I had spent and drop out with all the maybes of hopefully bringing my a level grades up, hopefully getting an offer for vet school etc. So I stuck it out, finished my degree, which was hard work when I didn't really want to be there and have eventually ended up at the RVC now doing what I should have done about 6 years ago.
Whilst being a graduate does have some merits in the way that I feel more ready maturity wise and academically to do the course now. But, it was a very long winded and expensive way to get that! Equally, plenty of people do manage the 'normal' route, so it is probably just a case of hindsight.
I would agree with the others in that whilst it is a big move, I would be inclined to drop out now. You can use it to show the uni's your motivation for being a vet and how much you have wanted to do this.
As the others have already said, grad entry whilst possible, is not as easy route by any means. It is fairly easy to get an offer from a high fee uni (edinburgh dont even interview grads), but it gets very competitive when you look at Nottm, RVC and Cambridge. Hence why a lot of grads end up going back and redoing a levels after their degree anyway to try and be competitive.
You don't get any funding for a second degree, whereas you would do it you dropped out of your first one in the first year. So all you get is a maintenance loan - that doesn't even cover my accommodation at the RVC.
Also, obviously some of the uni's do graduate entry (4yr degree programs) to take into your previous degree. They are *HARD*, I would say most people in my year are teetering on the edge of a nervous breakdown at the moment. Personally, if I was at the likes of Edinburgh on a 4 yr degree paying their fees per year I would have lost the plot by now. I am seriously worried about failing this year and having to resit - if I was paying £20k + per year I couldn't do that. The financial burden of doing this as a graduate should not be underestimated.
Anyway...good luck with what you decide.