Glushkov's death is coming a day after UK Prime Minister, Theresa May accused Russian Federation for being responsible for the poisoning of former spy Sergei Skripal and his daughter Yulia who are both said to be in critical condition.
Glushkov was a prominent opponent of the Kremlin.
The tabloid linked Glushkov to Andrey Lugovoy, the man who was accused of being behind the 2006 poisoning of former KGB spy Alexander Litvinenko with radioactive polonium.
The Metropolitan Police said there was no evidence to suggest a link between the poisoning and Glushkovs death.
Berezovsky was found hanged in his Berkshire home in 2013 in an apparent suicide.
Glushkov was sentenced in 2004 by the Savelovsky Court of Moscow to three years and three months in prison and released for time served, Russian news agency Tass reported.
The airline went on to pursue the case in London and Glushkov was due to attend a hearing on Monday morning at Londons Commercial Court but failed to appear.
"We stand in solidarity on this issue with our British friends", Gabriel said after discussing the matter with his British counterpart Boris Johnson.
Speaking to the Guardian at the time Glushkov said he was extremely sceptical Berezovsky had died of natural causes.
Ofcom said it had written to ANO TV Novosti, which holds RT's United Kingdom broadcast licenses, saying that if Russian Federation is found to be behind the attack, "we would consider this relevant to our ongoing duty to be satisfied that RT is fit and proper".
In recent years, Glushkov had lived in London, where he received political asylum. "Too many deaths [of Russian emigres] have been happening".
The minder told the Telegraph how his employer Glushkov had hatched an escape plan which included a hideaway should his life be put in danger.
One of his friends, the newspaper editor Damian Kudryavtsev, posted the news on his Facebook page. "Whilst we believe we know the identity of the deceased, formal identification is yet to take place", the police statement said.
The Russian embassy said it had sought Mr Glushkov's extradition in 2015 for committing a number of severe financial offences on the territory of Russia, but the British government refused.
She said Britain should look at wider and bigger personal sanctions beyond those in the U.S. Magnitsky Act which imposed visa bans and asset freezes on Russian officials. However, next of kin have been informed.
Still, the poisoning and now the unexplained death have resurfaced talk of what many see as a pattern of Russians who run afoul of the Kremlin and later die under suspicious or criminal circumstances.
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