It is not yet known how he died but his death has not been linked to the Salisbury poisoning case, the Metropolitan police said.
Nikolai Glushkov was discovered by his family and friends late on Monday night, The Guardian reported.
According to Egan, police knocked on her door in Kingston, southwest London, at 3.30 a.m. local time to ask whether she or her husband had seen or heard anything.
The London Ambulance service had called police after being summoned to a house in New Malden, where the man was found dead.
Counter-terrorism police are investigating an "unexplained" death of a man in his 60s found dead at a residential address in the London area, London police said Tuesday.
Police in London said they believed they knew the identity of the deceased man but that the body had not yet been formally identified.
WATCH: Video coverage of Sergei Skripal nerve-agent attack in the United Kingdom.
Glushkov's death came a week and a day after fellow Russian exile Sergei Skripal and his daughter Yulia were critically injured in a nerve agent attack in Salisbury. It is said to have been created by the former Soviet Union during the Cold War.
Russian officials have rejected the idea that their government is responsible for the attack on Skripal. The manner of death was classified as "Undetermined".
The émigré was acquainted with Russians who died in unexplained circumstances in the UK. As NPR's Mary Louise Kelly reported, "Traces of a rare, poisonous flowering plant were found in his stomach".
Read alsoSkripal poisoning: Trump says ready to condemn "Russia or whoever it may be " Berezovsky was once one of the most powerful businessmen in Russian Federation and was instrumental in Vladimir Putin's rise to power in 1999.
Berezovsky built a business empire valued in the billions before running afoul of the Kremlin and publicly denouncing Putin. That dispute was eventually settled in Abramovich's favor. "He was set to be a witness in a potentially explosive inquest in October into Litvinenko's death".
"You have the deaths of Boris and Badri over a short period of time".
Speaking to the Guardian at the time, Glushkov said he was extremely sceptical that Berezovsky took his own life, claiming that he was "killed". He added that the list of prominent Russians who opposed Putin was continuing to shrink: "I don't see anyone left on it apart from me".
Glushkov had worked for various Berezovsky enterprises including the vehicle factory AvtoVAZ and flagship Russian airline Aeroflot.
He is accused of organizing a large-scale fraud scheme, embezzling money from Russian Airlines. But by then, Berezovsky had moved to London. Glushkov, a close ally of Berezovsky, was twice charged with fraud in Russian Federation.