The fallout from the suspicious death of a former KGB agent in London reached the highest levels of Government this evening, as Britain's top ministers and security officials met to discuss the case.
The Cobra Cabinet emergency committee, which met after the July 7 bombings and the discovery of the alleged plot to blow up transatlantic aircraft this summer, convened after doctors found traces of polonium-210, a highly toxic radioactive substance, in the urine of Alexander Litvinenko, a former spy and critic of the Kremlin.
If - as Litvinenko himself claimed before his death last night - the Russian state apparatus is shown to have had a hand in the poisoning, Anglo-Russian relations would be thrown into crisis.
The Health Protection Agency, the body charged with protecting the public's health, described the apparently deliberate poisoning of Litvinenko on November 1 as an "unpredecented event" in the UK but said that the risk of exposure to those who came into contact with him was minimal.
Radiation experts and detectives from Scotland Yard's anti-terrorism branch fanned out across London after the presence of significant alpha radiation was found in Litvinenko's urine at around 6pm last night, said the chief executive of the HPA, Dr Pat Troop.
This evening, Scotland Yard confirmed that traces of the element, an extremely rare chemical that is relatively harmless unless ingested, inhaled or otherwise introduced to the bloodstream, had been found at Litvinenko's home in Muswell Hill, North London, and at the sushi bar in Piccadilly and the Millenium Mayfair hotel in Grosvenor Square, where the former spy held two meetings hours before falling ill.
"Detectives are carrying out an intensive investigation. We will trace possible witnesses, examine Mr Litvinenko's movements at relevant times, including when he first became ill and identify people he may have met. There will also be an extensive examination of CCTV footage," said Deputy Assistant Commissioner Peter Clarke, head of the Counter Terrorism Command, which is leading the investigation.
The identity of the poison dramatically catalysed the investigation into Litvinenko's death. Chemists said that a fatal dose of polonium could only be produced artificially, by a particle accelerator or nuclear reactor.
"This is not some random killing. This is not a tool chosen by a group of amateurs. These people had some serious resources behind them," Dr Andrea Sella, a lecturer in chemistry at University College London, told Reuters.
Earlier today, a statement dictated by Litvinenko in his last hours before losing consciousness accused President Vladimir Putin of his murder, an accusation made several times by fellow dissidents and friends of the former spy, a prominent critic of the war in Chechnya, since he fell ill.
The Foreign Office denied reports that it had held specific conversations with Moscow about the killing. A spokeswoman said the subject had been discussed during "routine meetings" with Russian embassy officials in London this week.
Walter Litvinenko, the former spy's father, who was with him when he died at 9.21pm last night, hours after radiation experts were first called to the London hospital, said that his son had been killed by "a little tiny nuclear bomb".
"It was so little that you could not see it. But the people who killed him have big nuclear bombs and missiles and those people should not be trusted."
Litvinenko became a British citizen last month, six years after he sought asylum in the UK after accusing the FSB, the successor to the KGB, of responsibility for terrorist attacks in Moscow that set off the second Chechen war.
Today, in a final statement dictated and signed two days before his death, Litvinenko said: "You may succeed in silencing one man but the howl of protest from around the world will reverberate, Mr Putin, in your ears for the rest of your life. May God forgive you for what you have done, not only to me but to beloved Russia and its people."
Mr Putin, in Helsinki for an EU-Russia summit, said that the death was a tragedy but that there was no proof that Litvinenko had died violently. He offered his condolences to the family of Litvinenko, like him a former Colonel in the KGB, but added: "This is not a violent death, so there is no ground for speculations of this kind."
Earlier, a Kremlin spokesman said that there was no need for Mr Putin to comment on allegations that Litvinenko's death was ordered by the Russian security services because the "allegations against Russia in this respect are nothing but nonsense".
The cause of Litvinenko's illness, which remorselessly attacked his immune system over the course of three weeks, baffled doctors, who first suspected thallium, and then a radioactive form of the metal, as the culprit, before admitting in recent days that they had little idea about the identity of the poison.
Suspicion among the former spy's friends and fellow dissidents has fallen on two meetings he held on the day he began to fall ill: a sushi meal with an Italian academic and security expert, Mario Scaramella, and a meeting, over tea, with two or three Russian businessmen, who included Andrei Lugovoi, another former KGB agent.
Speaking to The Times yesterday in Moscow, Mr Lugovoi denied any connection to the Litvinenko poisoning, saying that he had his own theories about who could be behind the attack: "I have my own opinion about that but it is too early to talk about it and it would be a mistake to do so. This is a very delicate issue since the secret services of both Britain and Russia have become involved."
