Berezovsky answered questions in English, but had a Russian interpreter with him in the witness box .
Acting for Abramovich is one of Britain's leading barristers, Jonathan Sumption, QC, who suggested that in post-communist Russia "a businessman like Mr Abramovich had no chance of building business interests without political influence".
Berezovsky said: "It depends on how smart he is and how much leverage he has. To get leverage you need to be smart - and he is not so."
Instead, Abramovich was "good at getting people to like him" and "good at psychology".
"He is good at appearing to be humble," he said. "He is happy to spend days just socialising with important or powerful people if that is what is needed so he can get closer to them."
Surrounded by lawyers, Abramovich listened through headphones to a Russian translation of proceedings.
He showed little reaction as the court heard how Berezovsky had been invited to join then Russian President Boris Yeltsin's "presidential tennis club" and began to exert political influence over the President through his daughter, Tatyana Dyachenko, and her soon-to-be husband, Valentin Yumashev, Yeltsin's chief of staff.
It is alleged that Berezovsky acted as a "political godfather" to Abramovich and supported Yeltsin in the 1996 presidential election through his TV network ORT.
In return for this support, the court has heard, Berezovsky persuaded Yeltsin to sell two state oil companies at auction, through which Abramovich built his fortune.
It is this, he has claimed, that entitles him to a share of the £7.4 billion Abramovich received when he sold Sibneft in 2005.
Outlining the nature of the agreement between Berezovsky and Yeltsin, Sumption said: "You will get the support of my television network and, in return, you will put me in a position where I can extract large sums of money from these two businesses."
"That is correct, yes." Berezovsky replied.
"Would it be fair to describe that as a corrupt bargain?" Sumption asked.
"Definitely not," Berezovsky said, who found himself in some difficulty when questioned about a libel action he brought against Forbes magazine in 2001 after an article in the magazine described him as a "corrupt and unscrupulous businessman, [who took] control of mass media companies for his own ends, both business and political".
Sumption produced witness statements from the trial in which Berezovsky denied exerting influence over Yeltsin - the matter on which his claim in this case depends.
"Why did you deny it and then sign a statement in support of your denial?" asked Sumption.
"That is a good question," Berezovsky replied, prompting laughter from Abramovich's lawyers.
"Yes," said Justice Gloster. "And it is a question which you will have to answer."
Berezovsky was shown his statement from the Forbes libel action, in which he said that after 1997 he no longer had any role in running Sibneft nor any shareholding in it.
His claim in the London case is that in 2001 Abramovich forced him to sell his Sibneft shares for less than they were worth.
Berezovsky apologised for his English several times and was frequently instructed by Sumption to answer the question he had been asked.
Abramovich claims that a £1.3 billion payment he made to Berezovsky in 2001 was an acknowledgement of his "debt of honour" to Berezovsky, whose political influence had made the creation of Sibneft possible, not a forced purchase of his stake, and that Berezovsky held no shares in the company.
Berezovsky is expected to answer questions until the end of next week, and Abramovich will give evidence next month.
- INDEPENDENT
