Sergei Skripal: latest in a series of mysterious exile tragedies
British police have so far found no evidence that former Russian spy Sergei Skripal, who is fighting for his life after being exposed to an unknown substance, was targeted by state actors.
But a series of suspicious deaths of high-profile Russians exiled in Britain has fuelled speculation that Moscow could be behind the collapse of the 66-year-old.
A former Russian double agent, Skripal has been living in Britain since a high-profile spy swap in 2010.
Skripal was sentenced to 13 years in jail in Russia in 2006 for betraying Russian intelligence agents to Britain's MI6 secret service.
He had been recruited by British intelligence while still an active officer with the Russian military's Main Intelligence Directorate (GRU) in the 1990s.
In July 2010, then Russian president Dmitry Medvedev signed a pardon for Skripal and three other Russians who were swapped for spies held by the United States.
Following are some other mysterious cases of Russian exiles in Britain.
- Alexander Litvinenko -
British Foreign Secretary Boris Johnson on Tuesday said the Skripal case had "echoes of death of Alexander Litvinenko in 2006", which caused a deep diplomatic rift between London and Moscow.
The agonising death of former Federal Service Bureau (FSB) spy Litvinenko by radioactive poisoning is the most high-profile of the exile incidents.
A British inquiry into the death said Russia's President Vladimir Putin "probably approved" the killing and identified two Russians, Andrei Lugovoi and Dmitri Kovtun, as the prime suspects in the polonium poisoning at a London restaurant.
- Berezovsky, Patarkatsishvili -
Litvinenko was a close friend of exiled Russian oligarch Boris Berezovsky, who also died in odd circumstances.
Berezovsky was found by one of his employees on the floor of the bathroom at his house in the upmarket town of Ascot, near London, in 2013.
A post-mortem found his death consistent with hanging but the coroner at the inquest recorded an open verdict.
In 2008, Berezovsky's Georgian business partner Badri Patarkatsishvili was found dead in his south London home, aged 52.
His death was put down to a heart attack, but Patarkatsishvili's fall-out with Putin and controversial political career in his home country raised suspicions of murder.
- Alexander Perepilichny -
In 2012, it was 44-year-old Russian businessman Alexander Perepilichny who was found dead in front of his London home.
It was assumed he had died of natural causes, probably a heart attack, but then police received a letter which urged a full investigation.
"We wrote a letter to the chief constable of Surrey to say he (Perepilichny) had been co-operating in a major case of transnational crime," says Bill Browder, head of the London-based hedge fund Hermitage Capital, which had significant interests in Russia.
According to Browder, Perepilichny provided the case with "lock-tight documentary evidence."
Two years after his death, Perepilichny's life insurance company ordered tests that detected a toxin from a Chinese plant called Gelsemium in his stomach, but his cause of death is yet to be determined.
In 2017, it was reported that US intelligence indicated that Perepilichny was likely "assassinated on direct orders from Putin or people close to him".
© 2018 AFP