A probe has been launched by counter-terrorism police amid reports a Russian exile who was a close friend of Putin critic Boris Berezovsky has been found dead.
Scotland Yard said a man in his 60s was found at a home in Clarence Avenue, New Malden, south-west London on Monday and that the cause of his death is unexplained.
The force said in a statement: "At this stage the Met Police Counter Terrorism Command is leading the investigation as a precaution because of associations that the man is believed to have had.
"There is no evidence to suggest a link to the incident in Salisbury."
Lawyer Andrei Borovkov told Russian media outlets on Tuesday that his client, Nikolai Glushkov, the former deputy director of airline Aeroflot, had died.
But he said he was unaware of the time and circumstances.
Neighbour Patricia Egan told the Press Association she was woken at 3.30am by the police.
"The door was banged this morning, it woke us up," the 65-year-old added.
"A policeman asked if we had seen or heard anything suspicious or did we hear the dog.
"There was a lot of police, about 10 cars.
"They didn't tell us what had happened, they just said there's been an incident.
"I'm just in shock - this nice neighbour, he was a lovely fellow."
She described him as well educated, said he had lived in the house for several years, and revealed that his daughter, who she thought was in her 20s, would visit.
"He told me she had gone to a Swiss finishing school, he said he was trying to force her to learn Russian," she added.
"He also had a son but he lived in Moscow I think."
She 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."
She described him as intelligent and very well-mannered, very generous and friendly, and that he had very good English.
Ms Egan also revealed he had an operation a few months ago on one of his legs for arthritis.
"He didn't go out much because of his illnesses, he had something wrong with his heart and had a few strokes," she added.
Three blue tents were erected in the front garden of the terraced house on Tuesday, with a police cordon also put in place.
Two police officers could be seen standing guard outside, with a number of officers in blue forensic suits also leaving the property.
At around 8.15pm a private ambulance reversed up to the tent as police vans shielded the view to the public, and a body was removed from the house.
Businessman Mr Glushkov was outspoken after the death of his friend Mr Berezovsky, telling the Guardian in 2013 he would "never believe" he took his own life.
Mr Berezovsky, a friend of murdered spy Alexander Litvinenko and thorn in the side of Russian President Vladimir Putin, was found hanged in the bathroom of his Berkshire home in 2013. An inquest recorded an open verdict.
Police and MI5 are to look into allegations that a string of deaths on UK soil may be linked to Russia, including the Berezovsky case.