Optimus SIM Adaptor Kit (compatible with Nano and Micro SIM Cards), for £1, at PoundWorld.
Compatible with any and all types of current SIM Card flavours that are out there within the Mobile sphere, hehe. :-)
I've seen these at Tottenham Hale Retail Park PoundWorld, as well as East Ham PoundWorld, and Shepherds Bush PoundWorld a few times also (Romford PoundWorld most likely has too, but haven't been down that side in quite a while to dispute otherwise?) .. but they are National. :-)
Worth getting at least one of these too I reckon?. :-)