Police are today investigating the "suspicious" sudden death in Britain of a billionaire Georgian businessman linked to leading Russian dissidents.
Badri Patarkatsishvili, 52, was found dead at his country mansion outside Leatherhead, Surrey, at about 11pm last night.
His family said he suffered a heart attack, but Surrey Police launched an investigation to confirm the exact cause of death.
Mr Patarkatsishvili - Georgia's richest man, with an estimated £6 billion fortune - spoke recently of his fears for his life after an alleged plot to murder him in London was uncovered.
One reported assassination plan bore chilling similarities to the killing of ex-KGB agent Alexander Litvinenko in 2006.
Mr Patarkatsishvili was a long-time business partner of Russian tycoon Boris Berezovsky, an outspoken Kremlin critic who now lives in exile in London.
Mr Berezovsky reported that the Georgian billionaire was not ill but had complained about his heart when he saw him yesterday.
A Surrey Police spokeswoman said today: "Police were called to an address in Leatherhead late yesterday evening following the collapse and death of Georgian businessman Badri Patarkatsishvili, believed to be 52 years of age.
"As with all unexplained deaths, it is being treated as suspicious.
"A post-mortem examination will be held later today to establish the cause of death."
Mr Patarkatsishvili's home, Downside Manor, is located in a leafy road in the countryside outside Leatherhead and is reported to be worth £10 million. Actor Michael Caine lives nearby.
Police cordoned off the property and were not letting anyone get close to it today.
Mr Patarkatsishvili amassed his wealth during the privatisation of state industries in Russia during the 1990s.
He helped to finance the "rose revolution" that swept President Mikhail Saakashvili to power in Georgia in 2003, but subsequently fell out with him.
Mr Patarkatsishvili - who founded opposition TV channel Imedi in 2002 - backed mass street protests against the government in Georgia's capital, Tbilisi, in November.
The demonstrations were violently broken up by police and Mr Patarkatsishvili left the country fearing arrest.
He was wanted in Georgia on charges of plotting to overthrow the government, which he denied.
He unsuccessfully ran against President Saakashvili in elections last month amid vote-rigging allegations.
In December he told the Sunday Times he did not feel safe returning to his home country.
The paper published extracts of a tape recording of a conversation said to have taken place between an official from the Georgian interior ministry and a possible hitman.
The two men allegedly discussed two options for making Mr Patarkatsishvili "disappear completely".
One involved murdering the tycoon during one of his regular visits to London and the other was to kill him as he flew in his private aeroplane to his castle in southern Georgia.
The official reportedly said Georgia wanted to be able to blame the assassination on Russia.
Asked whether he felt safe in Britain, Mr Patarkatsishvili told the Sunday Times: "I know about this tape and I was told it was very serious.
"I have 120 bodyguards but I know that's not enough. I don't feel safe anywhere and that is why I'm particularly not going to Georgia."
Scotland Yard, which investigated Mr Litvinenko's killing, is not involved in the inquiry into Mr Patarkatsishvili's death.
But a Metropolitan Police spokesman said: "It could be an option in the future."
Mr Berezovsky later released a statement in which he spoke of the "terrible tragedy" of losing his "closest friend".
He declined to speculate on what caused Mr Patarkatsishvili's death.
Mr Berezovsky said: "The death of Badri Patarkatsishvili is a terrible tragedy. I have lost my closest friend. This is a huge loss for all of his family and friends.
"I shall make no further comment on the circumstances of Badri's death. I shall wait for the authorities to complete their investigation."Reuse content