
That sounds about the price I would be charged at my vets. Because I have so many dogs I, at one time, was paying out more than £100 per month for drugs (for dogs on long term medication.) It was a member of the admin staff that took me to one side and said that I was their best dog customer, and should push for a discount.
I approached one of the partners and asked (nicely) what it would cost me for a prescription, as I was paying out so much every month. I was told to hang on and he would speak to the rep of these drugs to see if they would give me a discount. Eventually I was given a permanent 10% discount on all my bills (including boosters.) It's not an easy decision for me to buy from them, but I buy a lot of different meds, and would be charged a prescription fee for each and every one.
In your case, if it's the only drug you need, then it would be much more economical for you to pay £10 for a prescription.