hi GypsyGSD,
I think your case against animal welfare would be vry complicated but this is what I have found...
http://www.alaw.org.uk/temporaryitems/AWBUpdat e06.09.06.pdf
As it reads to me? as a main offence would be the unnecessary suffering of your dog via the drug that was administered via the vetinary surgeon whom did not inform you of the side effects.
The vet would argue that they took reasonable steps to ensure the needs of the animal were met.
All they would do, would be to improve their communication practices with the owners, and to bring any case would cost a small fortune.
I would suggest that you put pen to paper and read and re-read the letter you have written until you are satisfied that, if you were the receiver of the letter, that it read clearly and not of a grieving 'manical' pet owner.
I do not mean to sound harsh at all, I myself have sued the NHS. When you are close to the subject it is best to let a representative do the work for you.
My thoughts are with you as I have read about your dearest dog and I hurt for you.
B.