Deadly polonium traced to Russian nuclear plant

The claim comes on the day a postmortem examination took place on Litvinenko. Scotland Yard indicated that the result may not be available for several days because of tests to be carried out.

Investigators believe that while the former spy's assassination was not officially sanctioned by Vladimir Putin's government, the polonium 210 which killed him must have come from state nuclear laboratories.

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The killers must have had access to the laboratories, indicating a level of state involvement, according to intelligence sources. Reports say the source of the polonium 210 has now been traced by British scientists working at the Atomic Weapons Establishment at Aldermaston to a nuclear power plant in Russia.

Aldermaston scientists have been following the trail left by the polonium at 10 sites across London and on three British Airways planes that had been used between London and Moscow. One of the grounded BA planes was due to fly back to London for further inspection; the other two are already at Heathrow.

Lord Coe and Culture Secretary Tessa Jowell are expected to undergo health checks. The pair had flown to Barcelona on an Olympic fact-finding trip, boarding one of the two Boeing 767s currently grounded while undergoing radiation tests.

Ms Jowell said she had laughed when she found out she had flown on one of the "radioactive" planes. It was only when a sharp-eyed civil servant realised their aircraft was one of those involved in the radiation scare that Ms Jowell learned she could have been exposed to polonium 210.

"I'm not at all worried because I know the health risks are infinitesimally small," she said. "I don't expect to be tested. Seb and I and the whole Olympics team were on the flight, which was packed. It came as a surprise but we're among 33,000 or so people involved."

Nevertheless, the minister and her staff have been advised to go for medical tests if they feel ill.

About 33,000 people who took 221 flights across Europe between 25 October and 29 November may have been exposed to radiation although the risk to passengers is said to be extremely low. By last night, about 5,500 people had contacted BA.

A post-mortem examination will be carried out today at the Royal London Hospital with the medical team taking special precautions because of the nature of Mr Litvinenko's death. After the post mortem, his body will be released to his wife for burial.