Berezovsky: Latest in a series of mysterious exile deaths

But a series of suspicious deaths of Kremlin critics exiled in Britain is bound to fuel speculation about the 67-year-old tycoon's demise.

Berezovsky was found by one of his employees on the floor of his bathroom at the house in the upmarket town of Ascot, near London, on Saturday.

The fatality is the latest in a string of suspicious deaths befalling Russian exiles in Britain, the most high-profile being the agonising death of former Federal Service Bureau (FSB) spy Alexander Litvinenko by radioactive poisoning in 2006.

British police have named Andrei Lugovoi, a Russian lawmaker and former spy, as their chief suspect in Litvinenko's polonium poisoning at a London restaurant but Moscow has refused to extradite him to Britain.

Lugovoi has said he will no longer cooperate with the British inquest into the death of Litvinenko, who was a close friend of Berezovsky.

In 2008, Berezovsky's Georgian business partner Badri Patarkatsishvili was found dead in his south London home, aged 52.

His death was put down to a heart attack, but Patarkatsishvili's fall-out with Russian President Vladimir Putin and controversial political career in his home country raised suspicions of murder.

Last November, it was 44-year-old Russian businessman Alexander Perepelichny who was found dead in front of his London home.

It was assumed he had died of natural causes, probably a heart attack, but then police received a letter which urged a full investigation.

"We wrote a letter to the chief constable of Surrey to say he (Perepelichny) had been co-operating in a major case of transnational crime," says Bill Browder, head of the London-based hedge fund Hermitage Capital, which had significant interests in Russia.

Hermitage Capital had blown the whistle on what the company says was massive fraud by Russian state officials.

The chief whistleblower, lawyer Sergei Magnitsky, died in 2009 at 37, after spending 11 months on remand in squalid prisons.