British detectives were investigating today whether an exiled Georgian billionaire found dead in his mansion in Surrey last night died of natural causes or was the victim of an Alexander Litvinenko-style murder plot.

Badri Patarkatsishvili, Georgia's richest man and an unsuccessful opposition candidate in last month's presidential election, complained less than two months ago that he was the target of an assassination plan by his own government.

Police were called to his £10 million mansion near Leatherhead shortly before 11pm last night by his widow after the 52-year-old suffered a suspected heart attack. Today, his death with being investigated by Surrey Police's major crimes investigation unit under Detective Superintendent John Boshier.

"As with all unexpected deaths it is being treated as suspicious. A post-mortem examination will be held later today to establish the cause of death," Surrey Police said.

Mr Patarkatsishvili was worth an estimated £6 billion, much of it made as a partner of the Russian tycoon Boris Berezovsky, his fellow exile.

He funded an opposition campaign against Georgia's pro-Western leader Mikheil Saakashvili, and stood against him in last month's presidential election.

Georgia accused him of plotting a coup after airing a tape of him offering a $100 million bribe to a police chief to support opposition demonstrators - although Mr Patarkatsishvili's aides said that he had been the victim of entrapment.

He told The Sunday Times in December that Mr Saakashvili's regime was planning to send an assassin to kill him in London. He released a covert tape recording of negotiations between what he said was a Chechen warlord and an official from the Georgian Interior Ministry.

Mr Patarkatsishvili hired Lord Goldsmith, the former Attorney-General, to represent him as Georgian authorities mounted investigations into his business interests in the former Soviet republic.

Mr Berezovsky said today that his former business partner had complained about his heart when the pair met earlier yesterday, but he had not been ill.

He 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."

Mr Patarkatsishvili lived in Russia between 1993 and 2001. In the 1990s he was wanted by Russian authorities on charges of theft from the country's largest car factory, AvtoVAZ, which he ran with Mr Berezovsky.

He was also accused of plotting to arrange the escape from custody in 2001 of Nikolai Glushkov, deputy director of Aeroflot, Russia's national airline, who had been accused of fraud.

The man charged with breaking out Mr Glushkov was Andrei Lugovoy, who was arrested and jailed after the attempt failed. Mr Lugovoy is wanted by the British Crown Prosecution Service for the murder of Litvinenko, the dissident former Russian spy poisoned in London with radioactive polonium-210 in 2006.

Mr Lugovoy was responsible for protecting Mr Patarkatsishvili and Mr Berezovsky at the time as head of security at the Russian TV channel ORT, which the two men controlled.

Mr Patarkatsishvili remained good friends with Mr Lugovoy, a former KGB officer who is now a member of the Russian parliament. The pair were seen socialising together in Tbilisi, the Georgian capital, shortly before Mr Litvinenko was poisoned.

Mr Litvinenko also had links with the Georgian businessman. Sources in Tbilisi have told The Times that he stayed at Mr Patarkatshvili's residence in Georgia en route to Turkey when he fled Russia to seek asylum in London in 2000.

Russian prosecutors claim that Mr Litvinenko also visited Mr Patarkatsishvili as well as Mr Berezovsky in London shortly before he was poisoned. They accuse Mr Berezovsky of involvement in the murder of the former Federal Security Service (FSB) agent as part of a plot to damage President Putin's international image.

Georgia's former Defence Minister, Irakli Okruashvili, accused Mr Saakashvili of encouraging him to kill Mr Patarkatsishvili in 2005, although he later retracted the claim.

The tycoon helped to finance the "Rose Revolution" that swept Mr Saakashvili to power in Georgia in 2003, but the two men later fell out and he accused the President of turning into a dictator.

When Georgian police used teargas and rubber bullets to disperse opposition street protests in November, special forces troops also stormed the studios of Imedi TV and forced it to shut down. Mr Patarkatsishvili founded the station and News Corporation, which also owns The Times, was managing it at the time of the incident.

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