Oxana Mason, who has been Ms Izmestieva’s personal assistant for 12 years, told The Telegraph that she was an “absolutely beautiful and healthy woman”. 

Ms Mason said that she was the person who discovered Ms Izmestieva at her home in Kensington after becoming suspicious when she wasn’t answering her phone on Friday.

She let herself into Ms Izmestieva’s house with the spare key she owned and was the one who called police after finding her body.

‘A tragedy and nothing to do with politics’

Describing herself as Ms Izmestieva’s “closest friend in London”, Ms Mason said her friend’s death was “nothing to do with politics” and was simply “a tragedy that just happened”. 

She called the rumours of poisoning “absolute nonsense” and said her husband being in prison had “nothing to do with Irina’s death”. 

Ms Mason added: “She had nothing to do with politics at all, she’s living her life here in London, raising two beautiful girls and that is a tragedy and the first impression is that it’s likely something to do with the heart or with a blood clot.”

Ms Mason told The Telegraph: “I spoke to her on [November 10]  and she said she had a little bit of finger numbness and a little bit of heart pain … so it’s either [a] stroke – and that’s actually that’s what they said from the first glance.

“They said, it’s a natural death and it’s either stroke or blood clot. That’s what they told me the day when they found her. But an investigation will show.”

Ms Izmestieva was booked to have her first coronavirus vaccine on November 20 and was not unwell with the virus at the time of her death, Ms Mason said.

Suicide speculation dismissed as ‘nonsense’

When asked about the suicide speculation, Ms Mason said this was “absolute nonsense” and that she “loved her life here in London” and would have “no reason” to do that.

“She had a filmmaking company, she’s an absolutely beautiful and healthy woman who raised two beautiful daughters,” Ms Mason added.

Ms Izmestieva knew none of her neighbours in Cottesmore Gardens, according to Ms Mason, and was very much involved in London’s “Russian community”.

“I don’t like that her name was mixed with Russian politics,” Ms Mason said.

She added that she was currently arranging Ms Izmestieva’s funeral. 

Neighbours have reported seeing police, including officers in white forensic suits, and ambulance crews at the scene on Friday night, although Scotland Yard said on Wednesday it had no record of attending.

In a statement, London Ambulance Service said: “We were called at 7.11pm on Friday 12 November to reports of an incident at a residential address in Cottesmore Gardens, W8. We sent an ambulance crew and two medics in cars. Sadly, a person died at the scene.”

The cause of death remains unknown and a post mortem is still to be carried out.

Suspected foul play

Yevgeny Chichvarkin, a Russian businessman who moved to London more than a decade ago and lived next to Mrs Izmestieva between 2009 and 2013, wrote on Facebook that he suspected foul play.

“In the past few years Irina Izmestieva has been involved in a property dispute that I have no right to elaborate on,” he stated. “And now they found her dead after a new development in that dispute. I very much hope that British intelligence will hold a proper investigation so that we can hopefully know one day what happened. I can say for myself that she was a very healthy person.”

Mr Chichvarkin has said that Mr Izmestiev had been close to Vladimir Putin up until about 2005, when the president had even presented him with a gold metronome.