New York is home to 34 of the mega-rich, who are mostly American. Trailing behind are Moscow and San Franciso, with 20 billionaires each.

Forbes, the house magazine for the rich and powerful, believes that London’s appeal lies in its accessibility, stability, low-taxation and the global standing of City institutions.

Paul Maidment, from Forbes.com, said: “Many cities vie for the title of the world’s capital, but London still attracts the elite of the world’s rich and successful. And it can lay claim unchallenged to one title: it is the magnet for the world’s billionaires.”

At the top of the London list is Lakshmi Mittal, the world’s fifth richest person, according to Forbes’s current league table of the global elite. The Indian steel mogul has an estimated $23.5 billion (£12.27 billion) at his disposal.

He is ahead of Roman Abramovich, the Russian owner of Chelsea Football Club, who is the world’s 11th-richest person with a fortune estimated at $18.2 billion.

In third-place is Leonard Blavatnik, the Russian-American oil magnate, and Charlene de Carvalho-Heineken, a Dutch heiress to the Heineken beer fortune. Only then does the first British London-based billionaire make an appearance. David Reuben, who with his brother Simon, who lives elsewhere, has a net worth of $3.6 billion. They rank 185th on the list. Both were raised in Britain, but born in Bombay.

Mr Maidment said: “Billionaires are, by nature, a peripatetic lot. They can afford to own property on many continents and do. Their business interests and their investments are global.

“Their money travels the world as much as they do. On any day of the year, they are as likely to be in London or New York or Shanghai or Monaco. In a sense, they are citizens of no country but the self-contained universe of the super wealthy.

“Yet they do have to have the occasional points of contact with the rest of the world. London offers them a welcoming ecosystem.”

Other billionaire ex-pats in the capital are Philippe Foriel-Destezet, the Frenchman who founded the Adecco temp agency and the South African property developer, Donald Gordon. Also in London is Iceland’s first billionaire, Bjorgolfur Thor Bjorgolfsson.

“Low taxation is a big attraction. It is not stretching a point too far to say that for the super-rich London, is a tax haven,” Mr Maidment said.

“The UK’s tax laws contain provisions that enable non-British-born individuals who live in London, for some but not all the time, to be taxed only on their UK earnings.”

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