Warren Buffett, the legendary US investor, has toppled Bill Gates as the world's richest man, and Mark Zuckerberg, the 23-year-old Facebook founder, has been named the youngest billionaire in a survey published today by Forbes magazine.

The annual wealth survey said Mr Buffett, a close friend of Mr Gates who has donated billions of dollars to Microsoft founder's charitable Gates Foundation, held a fortune worth an estimated $62 billion dollars (£31.2 billion).

The philanthropist, who closed the gap on Mr Gates last year, saw his fortune leap by $10 billion after betting on Brazil’s currency as well as investing in PetroChina, the listed arm of China’s state-owned oil giant.

Meanwhile Mr Gates, who had held the top spot for 13 years, slipped down the list to third, amid a fall in the value of his Microsoft shares. Forbes estimated his wealth at $58 billion (£29.2 billion), up $2 billion on last year.

Second place went to Carlos Slim Helu, the Mexican telecoms magnate, with a fortune of $60 billion. For the first time, Forbes said, more than 1,000 people made it onto the billionaire list, with a combined wealth of $4.4 trillion.

A record 50 of the 1,125 entries are under the age of 40. Mark Zuckerberg, the 23-year-old founder of the social networking site Facebook, is the youngest billionaire, ranking 785th with $1.5 billion.

Lakshmi Mittal, the steel tycoon, was the leading UK resident, ranked fourth overall with a fortune estimated at $45 billion.

Like Mr Mittal, of the 51 British residents featured in the table, 20 are foreign nationals, or so called “non-doms”. Hans Rausing, the Swedish Tetra-Pak mogul is next, in at 77th, with a fortune of $10 billion.

John Fredriksen, the Cypriot oil tanker tycoon, and Leonard Blavatnik, the American industrialist, share 113th place, with an estimated $8 billion each.

The leading UK national is the Duke of Westminster in 46th place, with $14 billion.

Other prominent Britons include Philip Green, in 107th, with $8.4 billion, the Reuben brothers, who built their fortunes in the metals industry, in 178th with $5.5 billion, and Richard Branson, in 236th, with $4.4 billion.