An exiled Russian businessman associated with a leading critic of Vladimir Putin was murdered at his London home just over a week after a nerve agent attack on a former spy, police have revealed.

Investigators believe Nikolai Glushkov was strangled with a dog lead, a source told The Independent.

Officials say there is no evidence to suggest the Mr Glushkov's death and the attempted assassination of Sergei Skripal are linked, but the timing is likely to heighten tensions with the Kremlin just two days before presidential elections.

Mr Glushkov was found dead at his home in New Malden, south-west London, on Monday evening.

Scotland Yard initially treated the 68-year-old’s death as unexplained but a post-mortem examination gave the cause of death as “compression to the neck”.

“The Met Police’s Counter Terrorism Command, which has led the investigation from the outset, is now treating Mr Glushkov’s death as murder,” a spokesperson said.

“As a precaution, the command is retaining primacy for the investigation because of the associations Mr Glushkov is believed to have had.”

He was a close friend of exiled Russian oligarch Boris Berezovsky, who was himself a friend of murdered spy Alexander Litvinenko.

Mr Berezovsky was found hanged in the bathroom of his Berkshire home in 2013.

Police said a post-mortem showed no sign of a violent struggle, and an inquest recorded an open verdict after hearing conflicting evidence.

At the time, Mr Glushkov said he believed his friend had been murdered, telling The Guardian: “I don’t believe Boris died of natural causes. Too many deaths [of Russian exiles] have been happening.”

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Mr Berezovsky’s death is among up to 14 being reviewed by police and MI5 in light of the nerve agent attack on Mr Skripal and his daughter in Salisbury.

Mr Glushkov worked for Mr Berezovsky’s LogoVaz car company in Russia, before becoming the first deputy general director for Russia’s flag carrier Aeroflot in the late 1990s.

He served a five-year term for money laundering and fraud in Russia, then fled the country after being handed a two-year suspended sentence for fraud in 2006.

Last year, he was sentenced to eight years imprisonment and a 1 million ruble fine in absentia for allegedly defrauding Aeroflot – a case that continued at the time of his death.

Mr Glushkov, who has two children, was due to attend a commercial court hearing on Monday morning but did not arrive, sparking concerns among friends who later confirmed his death.

His LinkedIn page listed him as a “private consultant” in financial services since 2011.

Police described Mr Glushkov as a “retired financial director” and said he had lived in the home in Clarence Avenue for two years.

“At this stage there is nothing to suggest any link to the attempted murders in Salisbury, nor any evidence that he was poisoned,” a spokesperson said.

“Detectives are retaining an open mind and are appealing for any information that will assist the investigation into Mr Glushkov’s murder to contact them in confidence on 0800 789 321.

“In particular they are appealing for anyone who may have seen or heard anything suspicious at or near his home in Clarence Avenue, New Malden, between Sunday 11 March and Monday 12 March to contact them.

Skripal attack aftermath – in pictures Show all 15 1 / 15 Skripal attack aftermath – in pictures Skripal attack aftermath – in pictures Scene of attack Members of the emergency services in hazard suits fix the tent over the bench where Sergei and Yulia Skripal were found unconscious on a park bench in Salisbury in March 2018. Getty Skripal attack aftermath – in pictures Victim - Sergei Skripal The retired Russian colonel and former double agent for MI6 was in a critical condition in hospital for more than two months after being exposed to novichok in Salisbury. He was given refuge in the UK after being jailed in Moscow for treason. Mr Skripal came to Britain as part of a high-profile “spy swap” in 2010 in which four men were exchanged for ten Russian "sleeper agents" in the US. In this image he is speaking to his lawyer from behind bars in Moscow in 2006. AP Skripal attack aftermath – in pictures Victim - Yulia Skripal Yulia Skripal was struck down by a novichok poison alongside her father Sergei. Facebook Skripal attack aftermath – in pictures Scene of attack A police officer stands guard outside a branch of the Italian chain restaurant Zizzi where the pair dined at before falling ill. It was boarded off whilst investigators worked on the building and later found traces of the chemical weapon within it. AFP/Getty Skripal attack aftermath – in pictures Scene of attack Large areas of central Salisbury were cordoned off by police following the discovery of the Skripals. Traces of nerve agent were also found in The Mill pub. PA Skripal attack aftermath – in pictures Victim - Nick Bailey Detective Sergeant Nick Bailey, rushed to the aid of the Russian ex-spy and his daughter who were targeted with a nerve agent. He was hospitalized after aiding them and didn't leave until three weeks after the attack. Wiltshire Police/Rex Skripal attack aftermath – in pictures Police investigation - Skripal’s home Police believe they were poisoned at home, and detectives found the highest concentration of novichok on the front door of Mr Skripal’s house. Getty Skripal attack aftermath – in pictures Theresa May visits scene of attack Britain's Prime Minister Theresa May spokes with Wiltshire Police's Chief Constable Kier Pritchard near where the Skripal's were found. Britain expelled 23 Russian diplomats over the nerve agent poisoning and suspended high-level contacts, including for the World Cup on March 14. Theresa May told parliament that Russia had failed to respond to her demand for an explanation on how a Soviet-designed chemical, Novichok, was used in Salisbury. AFP/Getty Skripal attack aftermath – in pictures Skripal days before attack Sergei Skripal days before he was exposed to Novichok, that has left him fighting for life. ITV News Skripal attack aftermath – in pictures Police investigation - military involvement British soldiers were deployed soon after the attack to help a counter-terrorism investigation into the nerve agent attack. One of the places they were asked to help out with was Skripal's home and it's surrounding. They were asked to remove a vehicle connected to the agent attack in Salisbury, from a residential street in Gillingham. AFP/Getty Skripal attack aftermath – in pictures Police investigation Personnel in protective coveralls and breathing equipment cover an ambulance with a tarpaulin at the Salisbury District Hospital. AFP/Getty Skripal attack aftermath – in pictures Police investigation The investigation extended to the grave of Sergei Skripal's son Alexander in London Road cemetery. Getty Skripal attack aftermath – in pictures Police investigation The Counter Terrorism Policing Network requested assistance from the military to remove a number of vehicles and objects from Salisbury. EPA Skripal attack aftermath – in pictures Home Secretary visits scene of attack Home Secretary Amber Rudd visited the scene of the nerve agent attack at the Maltings shopping centre on 9 March. Getty Skripal attack aftermath – in pictures Yulia Skripal speaks for the first time Yulia Skripal, speaking for the first time, said she felt lucky to have survived the nerve agent attack in Salisbury which left her fighting for life. Ms Skripal said her life had been “turned upside down” by the assassination attempt. But the Russian national added she hoped to return to her homeland one day, despite the Kremlin being blamed for the attack. Reuters

“There are no wider public health concerns in relation to this investigation.”

Russia’s official Investigations Committee has launched its own criminal investigations into the attempted murder of the Skripals and Mr Glushkov’s death.

The Tass news agency quoted spokesperson Svetlana Petrenko as saying that the investigations “will be conducted in accordance with the Russian legislation and international law”, adding the committee was ready to cooperate with British law enforcement.

One of Mr Glushkov’s neighbours, Patricia Egan, said police had questioned local residents about what they had seen and heard of the businessman or his dog.

“I’m just in shock – this nice neighbour, he was a lovely fellow,” she added, recalling visits from his adult daughter.

“[Mr Glushkov] told me she had gone to a Swiss finishing school, he said he was trying to force her to learn Russian.

“He also had a son but he lived in Moscow I think.”

Ms Egan said Mr Glushkov was intelligent, educated, and well-mannered, generous and friendly, noting that he spoke very good English.

She also revealed he had an operation a few months ago on one of his legs for arthritis, adding: “He didn’t go out much because of his illnesses, he had something wrong with his heart and had a few strokes.”

Ms Egan said her neighbour’s birthday was on Christmas Eve and that they had “popped in for a glass of wine” to celebrate, adding that he “used to have a lot of people over”.

“It was a Russian house, all brown furniture,” Ms Egan added. “He told me he was from Georgia and always said how beautiful it was.”