At a rare briefing with reporters in a hotel suite in Shanghai, Mr Putin repeated his pledge to step down ahead of a presidential election in 2008 in accordance with a two-term limit in the constitution.

But he cast doubt on widespread assumptions that the two favourites to take his place are Sergei Ivanov, the Defence Minister, and Dmitry Medvedev, the chairman of the state gas monopoly, Gazprom.

“It could be someone whose name has not cropped up, someone other than those two,” said Mr Putin, calmly sipping cranberry juice as reporters were served cognac, wine and champagne.

Pressed on whether Russia’s top job could really pass to a complete unknown, he said: “Completely unknown? Not really. Such people are known to everyone but their names are simply not mentioned.”

His comments sparked a frenzy of speculation back in Moscow, where the succession question is rapidly becoming the single biggest concern for politicians and business people alike.

Mr Ivanov, a former KGB officer, and Mr Medvedev, a lawyer from St Petersburg, have been considered frontrunners ever since they were simultaneously promoted to be Deputy Prime Ministers in November.

However, Mr Ivanov, 52, has been plagued by scandals in the military, including the case of a young soldier who had his legs and genitals amputated after being beaten by elder conscripts.

Mr Medvedev, 40, although considered a superb administrator, is widely thought to lack charisma and leadership skills.

Now the spotlight has turned on two other potential candidates — Sergei Sobyanin, the presidential chief of staff, and Vladimir Yakunin, the head of the Russian railway.

Mr Sobyanin, 47, replaced Mr Medvedev as Mr Putin’s chief of staff in November and is now considered a frontrunner to be the next prime minister.

Mr Yakunin, 57, controls one of Russia’s most powerful monopolies and is said to be a close friend of Mr Putin.

The President’s real strategy, analysts say, may be to keep everyone guessing for as long as possible to avoid becoming a lame duck.

Vyacheslav Nikonov, head of the Politika Foundation, said: “As of now, anything said on this score is fortune-telling and nothing can be forecast by means of political analysis. But those who adhere to the two-successor version should remember that this contradicts Putin’s professional style.”

He said that Mr Putin, who has said he will personally name his successor, would announce the chosen candidate in the autumn of next year.

Other political pundits are still convinced that Mr Putin will seek a third term as he controls more than the two-thirds majority needed in parliament to change the Constitution.

An opinion poll this week showed that 59 per cent of the population was in favour of that option, reflecting ordinary Russians’ desire to prolong the current period of economic and political stability.

Some believe that Mr Putin will stand down in favour of a relatively weak successor in 2008, and then run for the presidency again in 2012.

Mark Urnov, head of the Expertise think-tank, said: “I still have doubts there won’t be a third term. The third term and the successor scenarios are equally probable.”

But whoever takes his place, and whenever that may be, Mr Putin had a word of advice for the next Russian President.

“If you make a mistake, you have to own up to it,” he said, before quickly adding that this did not apply to him since he had not made any.

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