Unwanted call centre calls: what can you do?

Cold callers are often an unwanted blight on people's lives. They invade privacy, they take your time up. The BBC's Panorama did a programme on them last week and now the US is taking steps to reduce the illegal automatic 'bots' which phone overseas - here's a link to the BBC story.

These calls have been illegal in the States since 2009. So what can you do about unwanted commercial calls?