Update: iTunes have issued me a refund, albeit with a rather terse email that implies it was my fault for signing up in the first place, but then goes on to say that iTunes Match isn’t available in the UK! Err!
This evening I installed iTunes 10.5.2 update on my Mac and was surprised to find that iTunes Match was presented as an option in the sidebar. I have a UK iTunes account and iTunes Match isn’t available here yet. I assumed that I just had good timing, and clicked on the option.