We have a BT phone which lets you screen everyone calling, and you press '1' if you know them or don't see some Bratislavian code displayed, otherwise they all get binned without us knowing, especially the foreign ones!
We bought it for when all the PPI scams were going on, and it was a huge success too! Funnily enough though, we did have a proper actual claim which was offered by our (then) bank by letter, and they paid up without a whimper, which was rather pleasant, as we cashed a cheque for well over £6,000, and that paid for our funerals...:0~