Badri Patarkatsishvili, a billionaire Georgian businessman and prominent opposition figure, has died in London of a heart attack, his spokesman has said.
Patarkatsishvili, 52, died at his home outside London overnight, Guga Kvitaishvili said on Wednesday.
Patarkatsishvili left Georgia in November and has spent time in Britain and Israel.
He was seen as a driving force behind anti-government protests in November and was under investigation at home on charges of plotting to overthrow the government.
He has denied the accusations but acknowledged offering large sums of money to police to side with protesters. The protests were violently broken up by police.
'Suspicious death'
A British police spokeswoman said on Wednesday that investigators were treating the death as suspicious.
"As with all unexpected deaths it is being treated as suspicious," a spokeswoman for the Surrey police said.
"A post mortem will be held later today to establish the cause of death."
London-based Russian tycoon Boris Berezovsky, a longtime business associate of Patarkatsishvili, said relatives told him Patarkatsishvili died around 11pm (2300GMT) on Tuesday of a heart attack.
Berezovsky, reached by telephone from Moscow, said that Patarkatsishvili had not been ill but had complained about his heart when they met on Tuesday.
"I saw him yesterday," Berezovsky said.
He said he had gone to the Georgian's home after learning of his death but that police were handling the matter and were not letting people in.
Patarkatsishvili ran against incumbent Mikhail Saakashvili in a snap election in January, getting about 7 per cent of the vote.
Opposition groups have alleged the vote that Saakashvili won with 53 per cent was rigged.