How much sleep do we really need? Tim Harford and sleep expert professor Matthew Walker test some of the claims.

Anxiety around sleep is widespread. Many of us feel we do not get enough. An army of experts has sprung up to help, and this week we test some of the claims from one of the most prominent among them, professor Matthew Walker. He plays ball and answers some of the criticisms of his bestselling book Why We Sleep.

(Photo: Person in bed reaches towards the alarm clock. Credit: Getty images)