I always use them, the stuff always arrives the next day, and they do very good prices
They really impressed me when I tried to return some liver tablets (vet said dog no longer needed them) - Royal Mail managed to trash the tablet box in the post so they wouldn't accept them back (fair enough) so vetuk sent them back to me free of charge to use in the future if I needed them. They were really helpful
i use http://www.wormers.co.uk/ for all my wormers (cat, dog & horse) and have never had any problems. They always send them out very quickly, usually next day but always within a couple of days.