Unsweetened chocolate

Does this exist in the UK?  Tesco only had bittersweet, and I thought I remembered someone saying that they brought it with them from the US.  Anyone know of a UK store that carries it?  Thanks 

I think I saw some at waitrose

I think that the Willy's wonky chocolate (not the correct name) actually market an unsweetened chocolate and you can find it in the baking section at Waitrose.  As a substitute I buy the chocolate with the highest % of cocoa solids that I can find, usually 72% (but there are higher %) and just cut down the sugar called for in the recipe, never been disappointed.

Thanks, Katydid, that's good advice.  My mom mixes cocoa and melted butter when she needs unsweetened chocolate and can't get it, but I have a recipe that calls for unsweetened, bittersweet, AND cocoa, so I wanted to get real unsweetened if I could, rather than substitute.  I'll have a look at Waitrose, thanks for the help!