Most chemists will sell them louise - they're commonly used by diabetics. They cost around a fiver for a pot that lasts ages. :)
Hi you can get them from Boots. But dont rely on them too much as your urine will be diluted with all the water your drinknig so the stix may not be as pink as yo want them to be.
I bought some in Superdrug and they didn't ask what I wanted them for.
No chemist has ever asked me what they're for (I'm diabetic so I've been buying them for ages). However, if they DO ask, you can either tell a little white porkie and say you're diabetic (that will stop all questioning instantly) or tell the truth and get embroiled in a discussion on the safety of VLCDs ... I know what I'D do! :)