This might help clarify things:
From the RCVS website
"Prescriptions for POM-V medicines may be issued only for animals under the care of the prescribing veterinary surgeon and following his or her clinical assessment of the animals"
"The Veterinary Medicines Regulations do not define the...
The official advice from the manufacturer is as follows
" Hay may delay the absorption of suxibuzone (danilon) and so the onset of clinical effect. It is advisable not to feed hay immediately prior to or with Danilon Equidos".