An Italian KGB expert who worked with poisoned former Russian spy Alexander Litvinenko has reportedly flown to London for radiation testing.
Mario Scaramella dined with Litvinenko on the night he is believed to have been slipped a deadly radioactive substance.
He is now in a safe house on the outskirts of London, Sky News reported.
Former KGB colonel Litvinenko, 44, a prominent critic of Russian President Vladimir Putin and a close friend of recently slain investigative reporter Anna Politkovskaya, died on Thursday, three weeks after meeting Scaramella in a London sushi bar.
Litvinenko, who claimed Putin bombed Moscow apartment blocks to justify launching a second war on Chechen separatists in 1999, said Putin ordered his and Politkovskaya's death.
Moscow denies involvement.
Politkovskaya, 48, who accused Putin of sanctioning torture and mass civilian killings in Chechnya, was gunned down in Moscow on October 7.
Scaramella, an advisor to a now-defunct Italian commission on Soviet spying in Italy, says he only had a drink in the Piccadilly Circus sushi bar. He says he had already eaten.
Shortly before the meeting, Scaramella says he showed Litvinenko threatening e-mails involving St.Petersburg gangsters suspected of carrying out contract killings.
Traces of polonium, the substance that killed Litvinenko, have been found at the sushi bar, Litvinenko's apartment, the adjacent offices of Russian emigre' billionaire and anti-Putin activist Boris Berezovsky, and the premises of a security and risk-management company, Erinys.
A British journalist who interviewed Scaramella after Litvinenko's death is also set to be tested for polonium.
British Prime Minister Tony Blair said Tuesday that "no political or diplomatic barrier" would hamper the probe into Litvinenko's death.
He said he would bring up the case with Putin at any "appropriate" time.
Eight Londoners out of 450 who contacted health authorities have already been sent for radiological scans and have shown external traces of polonium - which is only dangerous if ingested.
Britain's Health Protection Agency would not say Tuesday whether Scaramella had joined them.
London's Metropolitan Police did not confirm or deny Scaramella was with them.
Scaramella describes himself as an academic but has no current institutional affiliations. He started out as an environmental consultant before becoming a security expert investigating former Soviet espionage and possible nuclear trafficking.
Until earlier this year he worked with Italy's Mitrokhin Commission, set up by Silvio Berlusconi's former centre-right government, which trawled through the Italian part of a massive file of KGB contacts secretly compiled by Moscow archivist Vasily Mitrokhin.
The commission, which wound up in March, did not expose any former Communist public figures - despite frantic speculation in the right-wing press.
