Were ‘chillaxing’ to be made an Olympic sport, then David Cameron would be a dead cert for the gold medal, according to a new book.

Cameron: Practically a Conservative – written by journalists Frances Elliott and James Hanning - quotes an ally of the PM as saying: "If there was an Olympic gold medal for 'chillaxing', the Prime Minister would win it. He is capable of switching off in a way that almost no other politician I know of can."

The Conservative leader's ability to unwind and relax away from Whitehall is a key part of how he copes with the strains of the top job, the book says.

In a snapshot of Cameron's personal life, it reveals how he soothes the strenuous rigours of running the country by playing tennis against a machine nicknamed "the Clegger" and having a few glasses of wine with Sunday lunch.

The Prime Minister also enjoys a game of snooker while relaxing at the countryside retreat of Chequers and even has fun on his family's karaoke machine, according to the book, which is being serialised in The Times.

Describing Cameron's Sunday routine, the biography reveals how he checks the morning papers and internet and deals with any work-related queries before relaxing either in front of the television, on the vegetable patch, on the tennis court or with his children.

"He doesn't go back to obsessively checking the computer or rewriting the speech," the book says.

Other revelations include claims that Cameron has an "almost obsessive interest in the raw data of politics" and is a frequent visitor to political betting websites to keep up to date with the latest debates on polling methodology.