I've had this one a couple of times too Shona, I just hang up on them all - after all if it sounds too good to be true it probably is!!!

I have a caller display unit so never answer the phone to these numbers, I tend to get a lot of international ones too, those and 0800 no's. Blinking nuisance I think.

You don't need the phone number of who is called, to phone your provider and ring and complain!
We were getting prank calls from a with held number, so we phoned BT, who noted the number, and blocked it!

I get the "congratulations you have won a cruise " almost every day around 1pm