I use hyperdrug.com as well and recommend - not just for wormers for horses but for stuff like frontline for dogs and other stuff like witchhazel, hibiscrub, etc.
also they do cheap (and more expensive) rugs and human clothing. Catalogue is called Equine Pharmacy - so they will also 'fill' vets prescriptions cheaper than vet usually.
I use www.wormers-direct.com normally delievery time is around 3 days and they send an invoice so you dont pay until you recieve the item. I highly reccommend it
Watch prices though, the farmers co-op charge under £50.00 inc vat for 1litre of 10% suspension Panacur liquid, that Hyper-drug one is £35.00 for 500ml.
I use http://www.equi-store.co.uk/ as they have good prices and good delivery charges to Northern Ireland, some places will offer free delivery but once you put in NI at payment it will come up with as much as £5 delivery. This company charged me only 55p for 5 wormers. Lovely to deal with too.
Please do, they were the just the nicest people to deal with, answered emails late at night and dispatched immediately. Will definately be using them again..