Bought some Castrol oil from these blokes today, nice and cheap as I could pick it up in person with them being local to me; they are between Poole and Bournemouth. I don't know if it would work out much cheaper than other suppliers if you add on their postal charges (£5.50 for 2kg-25kg). The bloke also said they supply HiFlo filters and to let him know what I paid for mine next time and they would beat/match it.
http://moto-oil.co.uk/index.php?route=p ... 44_182_200