I had the same problem trying to buy Ketostix at Boots here in Linlithgow (scotland). The lassie at the till didnt know what i was talking about... she went through and got the chemist, who asked what i wanted them for. I told him to test for ketosis, and he said is it for a diet? I said yes, and he said "Boots wont let us sell them for that purpose".

Nevermind, there was another (independent) chemist further up the High Street, and i had no problem getting them there.