Yuganskneftegaz, the company’s main production unit, was sold for $9.35 billion (£4.7 billion), despite a US court order barring the auction and threats from Yukos shareholders to sue the winner.

“I think that the purchaser bought himself a nine billion dollar headache,” Alexandr Shadrin, a spokesman for Yukos, said after the sale.

Yugansk was forced under the hammer to help to cover Yukos’s $27.5 billion back tax bill, the result of an 18-month legal assault seen as the Kremlin’s way of punishing the company’s founder, Mikhail Khodorkovsky, for challenging its authority.

Mr Khodorkovsky, who had funded opposition parties and hinted at running for President, was arrested in October last year and is now on trial for tax evasion and fraud.

Gazpromneft, the oil-producing arm of the state-run gas monopoly Gazprom, had been widely expected to win the auction, paving the way for the formation of a state energy giant. However, in a surprise move, it withdrew from bidding and the only other participant, the unkown Baikal Finance Group, was declared the winner.

Virtually nothing is known about Baikal, except that it is registered in the city of Tver and applied to take part in the auction only a few days ago. Representatives of the company maintained a veil of secrecy, cancelling plans for a press conference by the winner of the auction.

Analysts said that they believed that it was a front for Gazprom or another firm controlled by the Government. According to some media reports, Baikal was registered at an address linked to Gazprom in Tver.

Either way, analysts said, the State had commandeered oil reserves of 11.63 billion barrels, or 17 per cent of Russia’s total, re-establishing control over a huge slice of an industry that is its main source of economic growth and international clout.

“By doing so, the State will have restored its previous control over a big piece of an industry that is not only the most important element in the local economy, but, along with natural gas, is increasingly the modern equivalent of military might,” Christopher Weafer, chief strategist at Alfa Bank, said.

The auction effectively reversed the controversial privatisation deal, in which Mr Khodorkovsky bought Yukos’s oil and gas fields at way below their market value in the mid-1990s.

It served as a chilling warning to Russia’s remaining oligarchs, who bought up the pillars of state industry for a song in the chaos that followed the collapse of the Soviet Union.

However, the destruction of Russia’s best-run firm has severely undermined confidence in the country’s investment climate and could jeopardise President Putin’s target of doubling GDP in a decade.

Igor Yurgens, a deputy head of the Russian Union of Industrialists and Entrepreneurs, the oligarchs’ lobbying group, told Ekho Moskvy radio that it was “unbecoming” for Russia that its top oil producer was bought by an unknown bidder.

Mr Shadrin, the Yukos spokesman, said: “Whoever stands behind the winner and gave it financial help has done irreparable damage to their reputation and subjected their business to significant legal risks.”

Lawyers for Yukos’s main shareholders, including Mr Khodorkovsky, said that the auction was simply expropriation and pledged to seek injunctions in foreign courts impounding Russian oil and gas exports.

A LONG FALL

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