Thanks so much for the advice and the link. They only charge €4 to ship to the UK so I'll be ordering a USB bit today.
It will be useful to use a USB power-pack when needed too. I just need Littlebits to release a Littlebits branded USB power pack (like their 9v battery) to finish off my littlebits collection. ARE YOU LISTENING LITTLEBITS?
I'm sure people would buy them!