I recently traveled to the UK and purchased a CTE sim card with unlimited data and I think 300 minutes? I wanted data service so I could use google maps to get around. Now that I'm in the US I have no use for the remaining 3 weeks or so.
It seems like a waste to just throw it out. If you are travelling to the UK soon and would like this SIM card, PM me your mailing address and I'll drop it in an envelope for you for free. It's the 'micro' size, but I have seen instructions to cut them down to nano online.
Cheers!