BORIS BEREZOVSKY, a Russian oligarch and fierce critic of the Kremlin, has lost his $6.5 billion lawsuit against fellow oligarch Roman Abramovich, the billionaire owner of Chelsea football club, after one of the most expensive court battles heard in Britain.

Mrs Justice Gloster, who presided over the four-month High Court battle, dismissed Mr Berezovsky’s claims in a ruling handed down yesterday that was seen as a humbling blow for the oligarch.

In the devastating ruling, the judge said Mr Berezovsky’s sworn evidence was at times “deliberately dishonest”. She described him as an “inherently unreliable witness, who regarded truth as a transitory, flexible concept, which could be moulded to suit his current purposes”.

By contrast, she said Mr Abramovich in his witness evidence gave “careful and truthful” answers and was a reliable witness.

The judge made it clear that her verdict boiled down to which of the two men she believed in a case in which there were no documents or contemporaneous notes to rely on. She concluded: “I regret to say that the bottom line of my analysis of Mr Berezovsky’s credibility is that he would have said almost anything to support his case.”

The case centred on claims that Mr Abramovich intimidated Mr Berezovsky into selling his oil and gas stakes, including his holding in oil group Sibneft, at a “gross undervalue” after Mr Berezovsky’s falling-out with Russian president Vladimir Putin. Mr Abramovich denied this and claimed he paid Mr Berezovsky $2.3 billion for krysha, or political protection, when he was building up his businesses.

The four-month trial shone an unforgiving spotlight on the chaos of Russia’s transition to a market economy, a period of lawlessness Mr Abramovich’s lawyer memorably likened to medieval England. It highlighted the lavish lifestyles of Russia’s mega-rich – the Caribbean cruises, the mansions and the art collections – in details that were lapped up not just in Britain but back in Russia.

While confirming much of what was already known of Russia’s post-communist business history, the case may alter perceptions of some elements.

One is the role of Mr Berezovsky himself. He gloried in his image as oligarchic kingpin – telling the Financial Times in 1996 that he and six other businessmen controlled half of Russia’s economy – years before anyone had heard of his publicity-shy partner. Mr Abramovich came to prominence only after 1999.

The judge read a summary of her ruling to the assembled media and to legal teams representing the two men but the full ruling will not be made public until at least mid-September, after it has been seen by the parties involved.

The case, which resulted in an estimated £100 million in legal costs, explored in forensic detail the events after the collapse of the Soviet Union, when vast swathes of state-owned assets were sold at knock-down prices to a small group of oligarchs.

Both oligarchs gave evidence during the trial. Mr Abramovich was not in the packed courtroom to hear the verdict, but Mr Berezovsky was present. – Copyright The Financial Times Limited 2012