Judge calls Berezovsky an unreliable witness after he loses case in which he claimed Chelsea owner cheated him out of £3bn

The Chelsea football club owner, Roman Abramovich, has won a high court action against his rival Russian oligarch Boris Berezovsky over a disputed £3bn debt.

Berezovsky, 66, was in the central London court to hear the judge, Mrs Justice Gloster, rule that he had lost his claim, which involved allegations of blackmail, breach of trust and breach of contract.

Abramovich, 45, who had denied the accusations, was not in the Rolls building courtroom to hear the final decision in the 10-month hearing.

Berezovsky, the former Kremlin insider turned bitter critic of Vladimir Putin, had claimed that Abramovich cheated him out of more than $5bn (£3.2bn) and "intimidated" him into selling shares in a Russian oil company at a fraction of their value. Abramovich, who remains on good terms with President Putin, said he did not owe Berezovsky anything.

It was the biggest private litigation battle in British legal history.

In her judgment, Gloster said the case "fell to be decided almost exclusively on the facts; very few issues of law were involved … The case was one where, in the ultimate analysis, the court had to decide whether to believe Mr Berezovsky or Mr Abramovich."

Berezovsky, she concluded, was not credible. "On my analysis of the entirety of the evidence, I found Mr Berezovsky an unimpressive, and inherently unreliable, witness, who regarded truth as a transitory, flexible concept, which could be moulded to suit his current purposes.

"At times the evidence which he gave was deliberately dishonest; sometimes he was clearly making his evidence up as he went along in response to the perceived difficulty in answering the questions in a manner consistent with his case.

"At other times, I gained the impression that he was not necessarily being deliberately dishonest, but had deluded himself into believing his own version of events. On occasions he tried to avoid answering questions by making long and irrelevant speeches, or by professing to have forgotten facts which he had been happy to record in his pleadings or witness statements."

By contrast, Abramovich, Gloster explained, "gave careful and thoughtful answers, which were focused on the specific issues about which he was being questioned. At all times, he was concerned to ensure that he understood the precise question, and the precise premise underlying the question which he was being asked.

"He was meticulous in making sure that, despite the difficulties of the translation process, he understood the sense of the questions which were being put to him.

"Where he had relevant knowledge, he was able to give full and detailed answers; he took care to distinguish between his own knowledge, reconstructed assumptions and speculation … In conclusion I found Mr Abramovich to be a truthful, and on the whole reliable, witness."

The judge found that the agreements between the two oligarchs were not as Berezovsky had portrayed them in his claims. "It follows that I dismiss Mr Berezovsky's claims both in relation to Sibneft and in relation to RusAl in their entirety," she said.

Speaking outside the court later, Berezovsky said: "I'm absolutely amazed at what has happened today. I'm surprised completely – particularly because Lady Gloster took responsibility for rewriting Russian history."

Asked whether he regretted bringing the legal action, he said: "I don't regret anything."

Berezovsky indicated that he might launch an appeal against the high court's decision but said he would have to speak to his lawyers first.

"When I came to the court I had prepared a phrase," he explained. "Churchill said that democracy is bad but there's nothing better. I was going to say an English court is bad but there's nothing better. Today I have doubts about whether that's accurate. Sometimes I have the impression that Putin himself wrote the judgment."

A statement issued on behalf of Abramovich said: "There were many serious allegations made against Mr Abramovich by Mr Berezovsky, including attacks on Mr Abramovich's honesty and integrity.

"We are pleased that the judge has firmly rejected all such allegations and has described Mr Abramovich as a truthful and frank witness who showed a responsible and honest approach when giving evidence in this case.

"We appreciate that, to many people, this case has been a uniquely Russian one, and should therefore have been heard in the Russian court system.

"Nevertheless, Mr Abramovich has always had great faith in the fairness of the English legal system and is both pleased and grateful for today's outcome.

"He stated from the outset that there was no merit to the allegations made by Mr Berezovsky, and this position has now been comprehensively vindicated by the court."