As a public inquiry into the death of Alexander Litvinenko gets underway, what do we know about the man and the circumstances surrounding his death?
On 1 Novermber 2006, Alexander Litvinenko took tea at a London hotel with former Russian agents Andrei Lugovoi and Dmitri Kovtun. Several hours later, Mr Litvinenko was admitted to a hospital in north London after complaining of feeling sick.
By 17 November Mr Litvinenko’s condition deteriorated and he was transferred to University College Hospital in central London and placed under armed guard.
Two days before his death, the Kremlin dismissed as “sheer nonsense” claims that the Russian government was involved in any alleged poisoning.
On 23 November 2006, Alexander Litvinenko died in care. Police said that they were investigating his “unexplained death”.
The key question that the inquiry will attempt to answer – just who is responsible for the death of Litvinenko? The health protection agency found that the former KGB spy had large quantities of the radioactive isotope polonium-210 in his body at the time of his death.
Months later, crown prosecutors named former Russian agent Andrei Lugovoi as the man suspected of murdering Litvinenko. Lugovoi had planned to travel to Spain with Litvinenko as part of his alleged investigation into Spanish links with the Russian mafia.
Dmitri Kovtun, who took tea with Mr Lugovoi and Mr Litvinenko at a London hotel three weeks before the death, was also named as a suspect. Mr Lugovoi and Mr Kovtun deny any responsibility for the death and Moscow has refused to extradite both men to the UK.
Mr Litvinenko reportedly joined the KGB in 1988. Ten years later, after apparently falling out with his employers over corruption within the Russian secret service, Litvinenko exposed an alleged plot to assassinate Russian tycoon Boris Berezovsky. He later spent nine months in remand before fleeing to London in 2000, where he is granted asylum.
At a news conference after Litvinenko’s death, Mr Lugovoi claimed that Litvinenko was a British spy who might have been killed by the British security services.
In 2012, a pre-inquest review was told that Mr Litvinenko was paid by MI6 and was working alongside Spanish spies in the days before his death.
When Litvinenko was killed in 2006, relations between the British and Russian governments were relatively good. The killing and accusations after turned the relationship bitterly cold.
Four Russian and four British diplomats were expelled from their respective embassies as a result of the dispute.
In 2013 the UK government rejected the idea of an inquiry suggested by the coroner in charge of the case, Sir Robert Owen. Litvinenko’s widow Marina said the rejection was a “political decision”, and Home Secretary Theresa May eventually admitted protecting “international relations” had played a part in the decision.
In February 2014 the high court overruled Theresa May’s decision not to hold an inquiry into Mr Litvinenko’s death.
Since the crisis in Ukraine begun last year, dialogue with the Kremlin has turned even frostier, and the UK government announced a public inquiry in July 2014.
In September, a directions hearing was told that the Russian government had refused to take part in the public inquiry.