Police had found radioactive traces at two more locations following the death of a Russian ex-spy as British authorities sought to quell fears among the public, after a handful of people were sent for tests. One of the locations with traces of polonium 210, the substance linked to the death last week of Kremlin critic Alexander Litvinenko, was the London office of exiled Russian oligarch Boris Berezovsky.
On the political front, Litvinenko's death, which his supporters claim was a Soviet-era type sting, is also increasingly threatening to strain relations between London and Moscow.
Speaking to lawmakers on Monday, Home Secretary John Reid confirmed that traces of the radioactive substance polonium 210 had been found in two hospitals where Litvinenko spent his dying days, a sushi bar and a hotel he visited on November 1, and "certain" other places in London.
A police spokesman told AFP on Tuesday that traces of polonium 210 had been found at an address on Grosvenor Street in the up-scale neighbourhood of Mayfair, and another on Down Street in west London, which Litvinenko's friend Alexander Goldfarb confirmed was Berezovsky's office.
The Daily Telegraph reported that the address on Grosvenor Street was the office of the private security firm Erinys.
The spokesman said that traces of the substance were also found at Litvinenko's home.
According to the BBC, police were also searching another property on Grosvenor street late on Monday, though the police spokesman declined to confirm or deny the report.
"There is no need for public alarm," Reid said in a hastily-arranged statement to parliament on the rapidly-evolving situation following the radioactive poisoning of Litvinenko.
"We are not yet even at the stage where the police have been telling me that there is definitely a third party involved in this," he added, repeatedly refusing to point the finger at Russia.
But in a sign of how seriously London is taking it, Reid again called a meeting of COBRA, the top security body which in the past has met for incidents including last year's July 7 terrorist attacks, to assess the risks.
The COBRA security body first met last Thursday, the day the 43-year-old ex-spy finally succumbed to a mysterious illness which struck him down on November 1, shortly after he met two unidentified Russians in a London hotel.
In a letter read out by his spokesman the morning after his death, Litvinenko bluntly accused Russian President Vladimir Putin of his "barbaric" killing.
Putin has dismissed the allegations as "political provocations" from critics, adding: "I hope British authorities will not allow the fueling of political scandals."
At the weekend one government minister, Northern Ireland Secretary Peter Hain, voiced concern about some "extremely murky murders of the senior Russian journalist," referring to the death of Kremlin critic Anna Politkovskaya.
Britain has already asked Russia, via its ambassador in London, for any information on the unprecedented killing, which critics blame on Moscow, pointing out the difficulty of obtaining polonium 210.
But Reid was careful not to fuel the diplomatic fire on Monday, noting the diplomatic request to Moscow and refusing to be drawn despite repeated questioning by opposition lawmakers.
"I think it would be unwise for me to ... start pointing fingers," he said.
Reid also confirmed that health authorities had so far sent three people for radiological tests, after some 500 people rang a helpline over the weekend concerned that they may have been contaminated.
The Health Protection Agency (HPA) has also sought to allay concern, pointing out that the kind of alpha radiation involved can only travel tiny distances, so the risk of contamination is minimal.
Also on Monday officials confirmed that an inquest into Litvinenko's death will be formally opened on Thursday.
The formal inquiry is likely to adjourn shortly after being opened, since the full inquest will have to wait until the police investigation has been completed.
Doctors have postponed carrying out a post-mortem on Litvinenko due to safety fears for the medics involved.
