The 67-year-old – who was a renowned critic of Russian president Vladimir Putin – was found dead in his bathtub according to reports.
He had previously survived numerous assassination attempts.
“Yes. he is dead. It was confirmed to me by his private lawyer this afternoon,” Berezovsky’s spokesman Tim Bell told AFP by telephone.
A spokesperson for the Russian president said that Berezovsky had asked Putin for forgiveness and permission to return to Russia shortly before his death.
Berezovsky, who made his fortune in the aftermath of the break-up of the Soviet Union in the early 90s, saw his fortunes decline when Putin became president.
He had lived in the UK since 2000.
“Some time ago, maybe a couple of months back, Berezovsky sent Putin a letter that he personally wrote in which he said that he realises that he had committed a great number of mistakes,” Kremlin spokesman Dmitry Peskov told Russian state television.
“He asked Putin for forgiveness for his mistakes and asked him to obtain the opportunity to return to the motherland.”
It is not clear how Putin responded to the letter but the spokesman added that the Russian leader had been informed of Berezovsky’s death.
Mr Berezovsky’s claims against Russian billionaire Roman Abramovich were dismissed in cour
Last year, the former Kremlin advisor lost a high-profile court battle with fellow billionaire and Chelsea Football Club owner Roman Abramovich in which he had claimed he was bullied into selling shares in the oil company Sibneft.
He was ordered to pay nearly $5 million in damages.
For years Berezovsky was at the centre of a group of anti-Putin exiles in London who included Russian dissident Alexander Litvinenko, who died of poisoning by radioactive polonium in November 2006.
Former Russian spy Alexander Litvinenko, who was poisoned, was a close associate of the Russian tycoon
Just two weeks ago, Andrei Lugovoi, a former FSB agent regarded by Britain as the prime suspect in Litvinenko’s murder, accused Berezovsky of being behind the gruesome murder.
Berezovky’s death comes as Britain and Russia are trying to mend their relations, which were chilled in the wake of the Litvinenko killing.
Lord Bell, a leading public relations and advertising expert, told The Daily Telegraph: ‘He was a very close friend and a very nice man, very kind to me and to the people around him.’
Russian billionaire Boris Berezovsky built up legal costs totalling more than £250,000 after becoming embroiled in a case at the same court with his former partner, Elena Gorbunova
His career traced the arc of Russian society from the dawn of free enterprise in the Soviet Union’s dying days to the oligarch-dominated 1990s, then the return of state control in the first decade of the new millennium.
Born on January 23, 1946, Berezovsky graduated from a Moscow forestry institute then spent nearly two decades as a quiet academic before becoming a car dealer in the late 1980s and a billionaire oligarch by the following decade.
Putin began his presidency in 2000 by warning that the heyday of super-rich powerbrokers like Berezovsky was over. Berezovsky fled into exile that November, just in time to escape arrest on fraud charges.
In London, he became the Kremlin’s greatest nemesis, mockingly defying years of attempts to extradite him. He emerged from an extradition hearing in 2003 wearing a Putin mask.