Millions watched as Roman Abramovich suffered the agony of defeat alongside Chelsea fans. They knew him from the gossip, sport and news pages, in which he regularly crops up spending millions on art or enjoying London's nightlife, with his beautiful girlfriend on his arm.

Yet the Russian billionaire remains an enigma. Little is known about where his vast fortune came from, or about his complex relationship with Russia's rulers, and in particular with Vladimir Putin, the former President.

Today The Times can disclose that Alexander Litvinenko, the spy poisoned in Britain in a suspected Russian plot, made the astonishing suggestion that Mr Abramovich effectively vetted Mr Putin - on behalf of Russia's powerful oligarchs - to succeed Boris Yeltsin as President.

Litvinenko also told The Times that the football-loving billionaire controlled so much of Russia's economy that he was in danger of being killed by the Kremlin's special services.

He said in his broken English: “Mr Abramovich have good contact with Putin before Putin was President. Russia oligarch select people who will be President. In 1997-98 Mr Abramovich was the best person who is check these candidates to be President. Now Mr Abramovich has good relationship with Putin.”

Mr Putin took over as acting president in 1999 and won the post in an election the following year. Mr Litvinenko added that the football chief helped to fund his campaign.

Mr Litvinenko, a former KGB man and an outspoken critic of Mr Putin, died of radiation poisoning in London in 2006 after being contaminated with polonium-210.

His words are given an intriguing new significance by a Commercial Court battle in London between Mr Abramovich and the exile Boris Berezovsky over $4 billion (£2 billion) of Russia's oil and aluminium riches.

Mr Litvinenko met Mr Abramovich through a business club run by Mr Berezovsky. Mr Putin was summoned to the Kremlin in 1996 to serve in high office under President Yeltsin at a time when Mr Berezovsky was the President's close aide and Mr Abramovich, in turn, was an ally of Mr Berezovsky.

In an unpublished interview two years before his death, Mr Litvinenko said: “I know Putin's team since 1991 in St Petersburg. I know who Mr Putin is. I have meetings with Putin 1998. In 1999, my way and Mr Abramovich were different. Mr Abramovich stayed near Mr Putin. Who has stayed near Mr Putin for five years?”

According to a biography, Abramovich: the Billionaire from Nowhere, Mr Abramovich interviewed the candidates for Mr Putin's first Cabinet in 1999. But the claim that he effectively vetted Mr Putin too goes farther than any previous account.

Mr Litvinenko believed that the Chelsea boss was in danger from a corrupt mafia around President Putin. “Mr Abramovich in the future 100 per cent have a lot of problems from Russia special service,” the spy said. “Maybe killed, maybe put in prison. Maybe push under contracts.”

Mr Litvinenko made his remarks in a telephone interview with The Times, which at the time was investigating the sources of Mr Abramovich's £12billion fortune.

Only businessmen tolerated by the security services could survive in Russia, he suggested. Others, such as the billionaire Mikhail Khodorkovsky, found themselves prosecuted for corruption and jailed.

“Abramovich is not political. He is not philosopher. He is fortune,” Mr Litvinenko said. He added that Mr Abramovich may have become too powerful a businessman for the security services to tolerate.

“[He] took a lot of Russian commercial company under himself,” he said. Mr Litvinenko gave warning that Russia's special services would remove Mr Abramovich by killing or imprisoning him or taking out a contract. If he tried to flee, they would get him back by seeking his extradition on some crime charge.

“If Mr Abramovich escapes from Russia and takes his money, if he is like control his money, Russia special service send crime case to this country where Mr Abramovich stayed.”

In the event, a more peaceful solution was found. Mr Abramovich went on to divest himself of Russian assets, selling his oil business Sibneft to the Russian State for £6.6billion in 2005.

The Times put the allegations to Mr Abramovich's spokesmen but they declined to comment.

Mr Litvinenko's own downfall came after he antagonised Mr Putin, at the time head of the FSB, the successor to the KGB, by staging a televised press conference in 1998 amd announcing that the FSB had ordered the assassination of Mr Berezovsky.

After being jailed and freed several times, Mr Litvinenko fled Russia.

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