Facebook is so concerned about the safety of boss Mark Zuckerberg that his security costs are now more than ten times those of British prime ministers.

The reclusive social media tycoon famously spent $43 million (£21 million) on the four homes nearest to his Silicon Valley mansion to guarantee privacy.

And now Facebook's latest annual report reveals it shelled out $3.6 million (£2.9m) last year on protection at those properties and when Zuckerberg was travelling. This has risen by £1.2m since 2013 - compared to the £250,000 annual cost of protecting prime ministers.

Zuckerberg, who is worth $50 billion, takes a $1 salary, but accounts reveal he picks up $7 million a year in other compensation. As well as the security bill, this includes half a million pounds to cover the costs of a private jet.