Four people in Germany are being tested for polonium-210 contamination after traces of the radioactive substance were found in the homes used by a contact of Alexander Litvinenko.

Police in Hamburg said the four people were related or linked to Dmiti Kovtun, a Russian businessman who met Litvinenko in a London hotel on the day he fell ill.

They are understood to be Kovtun’s ex-wife, her two small children aged one and three, and her boyfriend.

As a precautionary measure they been taken to hospital in Hamburg to ascertain whether they have ingested any radioactive material.

"With the four people mentioned in the close circle of Mr Kovtun, there is the suspicion that this might possibly have entered their bodies," said Thomas Menzel, the policeman who is leading the German investigation.

He said they were undergoing further tests.

German police said yesterday that Kovtun had left a trail of polonium in Hamburg - including in a car, an office and his ex-wife’s house, before he flew to Britain to meet with Litvinenko.

There were traces of the substance found on a desk and chair in the apartment belonging to Kovtun’s ex-wife and in a bed and on a chair at the villa of his Eleonora Wall, his former mother-in-law.

Mr Kovtun, a former officer of the Russian Federal Security Service (FSB) is said to be seriously ill but has stated that he believes he is a victim of the same plot which killed Mr Litvinenko.

"Much is contaminated - my body, my clothes, my office in Moscow, it's simply everywhere," he told the Der Spiegel news service.

Hamburg has been ruled out by police as a base for the plot against Litvinenko and Scotland Yard detectives in Moscow today met with Andrei Lugovoy, an ex-KGB bodyguard who was the other man who met with Mr Litvinenko on the day the poisoning is said to have taken place. Mr Litvinenko died 22 days later.

Lugovoy has repeatedly declared he has played no part in Mr Litvinenko's death and has claimed he has been set up.

Lugovoy has suffered radiation contamination, but his condition has been described as stable.

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