Nikolai Glushkov was found dead Monday night.
They added there is no evidence to suggest the death is linked to the incident in Salisbury, where a former Russian spy Sergei Skripal and his daughter Yulia were poisoned with nerve agent which the United Kingdom government believes came from Russia.
But he is believed to be Nikolai Glushkov - a friend of the late Russian oligarch Boris Beresovsky, who criticised President Vladimir Putin.
Glushkov had lived in London in recent years, after being granted political asylum in Britain.
Police are describing his death as "unexplained".
Mr Glushkov is said to have not believed his friend had taken his own life, and told the Guardian: 'Too many deaths [of Russian emigres] have been happening'.
Sky News' home affairs correspondent, Mark White, said Mr Glushkov's home in New Malden, southwest London, is being treated as a crime scene.
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Tillerson, formerly the CEO of ExxonMobil, was out of the country, finishing a week-long tour of several African nations. In October, NBC news reported that Tillerson called the president a "moron", something Tillerson never actually denied.
Glushkov, who has been an executive at state airline Aeroflot and also worked for Berezovsky's vehicle company LogoVAZ, followed and was granted asylum in 2010.
Berezovsky was found dead in March 2013 with a scarf tied around his neck in the bathroom of a luxury mansion in Ascot, an affluent English town near the Queen's Windsor Castle, west of London.
The news was confirmed Tuesday on Facebook by Moscow Times board member Damian Kudryavtsev, who was close to both Glushkov and Berezovsky.
Counter-terrorism police are investigating the death as a precaution because of the associations that the man, aged in his 60s, is believed to have had.
Berezovsky is one of 14 Russians whom U.S. intelligence services believe were assassinated in the United Kingdom, according to an investigation by BuzzFeed News. "[But] I don't believe it was suicide", he said.
Litvinenko died after being poisoned with Polonium-210 in London in 2006, while Georgian businessman Patarkatsishvili was killed in Leatherhead in 2008.
United Kingdom counter-terror police are investigating the "unexplained death" of a Russian businessman in London.