I think it would be best if you concentrated on getting good grades in your current A-levels, then afterwards consider doing a fast track A-level(one year) in Biology or Chemistry or even both. You could always apply to do a three year BSc in science which will then(dependent on the grade you get) lead to a graduate option to study as a Veternary surgeon.
This is not the end of your veterinary career if its what you really want! I myself am facing a similar dilemma after nearly 3 years of a BA Egyptology and Ancient History degree i have decided to pursue my childhood aspirations to become a Vet. I, like you, took non-science related A-levels, including English and History.
Luckily for you, you are still pre-application to a University, as i said have a look at some of the gradate programs the Veterinary faculties offer, they may be even more competitive than the already competitive Veterinary Medicine 6 year degrees, but if its your dream then its your dream. I would definitely look into a 3yr BSc in some form of Animal biology degree, Veterinary schools also like Biochemistry!
Hopefully the requirements for such courses won't include science related A-levels, however even if they did it would still be worth applying.
If you are not accepted try getting a place at Warwickshire College [
www.warwickshire.ac.uk]
It has an extensive amount of Animal courses, Pershore(where many animal course are held) has wonderful facilities including hands on with animals...including a llama(i know i've seen him).
You can do a science degree here, or a 2 year HND which can then be topped up by a BSc at this university or the university of Worcester. If you feel its all just too much there is also Veterinary nursing, which if you love animals and just want to work with them, its worth considering.
Best wishes
Louise