The case has triggered memories of the death by radioactive poisoning of Kremlin opponent Alexander Litvinenko in 2006, which have severely strained diplomatic ties between London and Moscow.
However, a police spokeswoman said no radioactivity had been found in initial investigations into the death.
She said: "As a result of the initial work by the detective there is no suggestion of radioactive material involved."
An ambulance was called to Patarkatsishvili's house late on Tuesday evening after Patarkatsishvili fell ill while entertaining a large number of friends and family, police said.
"As far as I know from his relatives, it was his heart," exiled Russian billionaire Boris Berezovsky, a friend and business partner, told Reuters by phone from Britain.
|Patarkatsishvili denied |
he plotted a coup [AFP]
In a separate statement, Berezovsky said it was a "terrible tragedy. I have lost my closest friend."
Patarkatsishvili's allies in Tbilisi, Georgia's capital, have called for international experts to launch an inquiry.
The millionaire had left Georgia in November and had spent time in Britain and Israel.
He was seen as a driving force behind anti-government protests in Georgia in November and was under investigation at home on charges of plotting to overthrow the government.
He had denied the accusations, but acknowledged offering large sums of money to police to side with protesters.
The protests were violently broken up by police.
Patarkatsishvili ran as a candidate in Georgia's presidential election in January, winning seven per cent of votes, but did not campaign in his homeland for fear of detention.
Eduard Shevardnadze, the former Georgian president and Soviet foreign minister, said: "His death is a big loss for our country. I know he wanted to do a lot of good things for Georgia."
Patarkatsishvili held meetings with his public relations team in central London on Tuesday and showed no obvious signs of illness, a person who attended the meeting said.
Rati Shartava, a Tbilisi-based aide to Patarkatsishvili, blamed legal charges brought by Mikhail Saakashvili's, the Georgian president, for triggering his death.
"The state machine fought him and his heart gave in," Shartava said.
Georgian government officials declined immediate comment on the death.