Hi,
Since you already have had contact with a veterinary practice where, you presumably take your own animals, you have a head start.
If you seriously wish to study veterinary science you will need A level Biology, Chemistry and Physics as well as a good renge of subjects at O level GCSE. Unless you think you can achieve this you have no chance.
Assuming that you can, write to the senior partner in the practice - Mr or Mrs Hart at the Hart Veterinary Centre or Mr Cornish or Mr Ferens at Bicester Vet Centre, whichever you attend, saying that you are interested in becoming a vet, and asking if you could 'see practice' at weekends for a little while.
Good luck,
W