Nikolai Glushkov's death comes amid heightened concern following a nerve agent attack on a former Russian spy in England and as the government said it would investigate the deaths of a number of Russia-linked individuals which have raised suspicions.
Nikolai Glushkov was found dead by family and friends at his home in London on Monday, The Guardian reported.
Sky News' home affairs correspondent, Mark White, said Mr Glushkov's home in New Malden, southwest London, is being treated as a crime scene.
It added that there was "no evidence to suggest a link to the incident in Salisbury". He was known as the "godfather of the Kremlin" before fleeing to London in 2000 after a row with Russian leader Vladimir Putin.More news: US Deaths Tied to 'Ubiquitous but Insidious' Lead: 410K a Year
The Met said officers believe they know who the man is, but he is yet to be formally identified.
The 68-year-old Glushkov was a businessman in Russian Federation after the fall of Communism and had been a close associate of oligarch Boris Berezovsky, who was forced to flee Moscow after falling out with Vladimir Putin.
Glushkov said: "You have the deaths of Boris and Badri over a short period of time".
Glushkov had worked for Russian airline Aeroflot and at Berezovksy's LogoVAZ auto company.More news: HBO is throwing everything into Game of Thrones spinoffs
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.
Glushkov was subsequently charged with money laundering and fraud and served five years in jail in Russian Federation.
Speaking to the Guardian at the time, Glushkov said he was extremely sceptical that Berezovsky took his own life, claiming that he was "killed".More news: Katy Perry Shocks 'American Idol' Contestant with First Kiss