Nov. 27 (Bloomberg) -- U.K. health authorities will test three people showing potential symptoms of radiation exposure less than a week after former Russian spy Alexander Litvinenko died in a London hospital with a ``significant quantity'' of the radioactive polonium 210 isotope in his body.

Litvinenko died on Nov. 23, more than three weeks after becoming ill. In a message he wrote before he lost consciousness, Litvinenko, who had become a British citizen, said he was poisoned because of his criticism of Russian President Vladimir Putin's government, a charge denied by the leader.

The Itsu sushi restaurant in London's Piccadilly, where Litvinenko met with a friend on Nov. 1, was being decontaminated and tests for radioactivity were also being carried out at a number of locations visited by Litvinenko, including the Millennium Hotel Mayfair in Grosvenor Square, the Health Protection Agency said today in a statement on its Web site.

The three people were among more than 450 people who called a National Health Service Direct helpline, at +44-845-4647, in response to the Litvinenko case, a spokeswoman for the agency said today in a telephone interview. Of the callers, 18 were initially forwarded for further scrutiny, and a decision was made to test three of them, she said. She declined to further identify the people or the clinic where they will be tested.

``A monitoring program has started for the patient's family and others who may be at risk,'' the National Health Service said in an undated statement on its Web site. Litvinenko had one son with his wife, Marina.

Restaurant, Hotel

As well as the hotel, the restaurant, and Litvinenko's home in Muswell Hill, north London, some indication of radiation has been found in ``several other premises,'' U.K. Home Secretary John Reid told Parliament today. Part of the intensive care unit at University College Hospital, where the former spy was treated, remains closed, he said. Traces of the polonium isotope have been found in an office block in west London and a building in London's Mayfair District, the British Broadcasting Corp. said.

Litvinenko first reported feeling ill on Nov. 1 after meeting with a friend at Itsu. Later that day, he also went to the Millennium Hotel. Mario Scaramella, an Italian, said at a Nov. 21 news conference in Rome that he was the friend at Itsu. Scaramella said he and Litvinenko had both received e-mailed threats days before the former spy's illness began.

Itsu said on its Web site that none of the workers at its Piccadilly branch was showing signs of ill health, and that it is cooperating with authorities. Millennium & Copthorne Hotels Plc said in an e-mailed statement that staff at its Millennium Hotel Mayfair are ``working closely'' with authorities.

Inquest

An inquest into Litvinenko's death may start on Nov. 30, Matt Cornish, a spokesman for Camden Council, a London municipal authority, said in a telephone interview, adding the date ``isn't set in stone.''

Sudden or unnatural deaths in the U.K. are usually subject to an inquiry by a coroner, who must establish the medical cause of death. The inquest will be carried out by the St. Pancras Coroner's Court in North London's Camden district. Lee Gronow, a coroner's officer at the St. Pancras Coroner's Court said in a phone interview that Dr. Andrew Reid, the coroner, hasn't yet given instructions on when the inquest will begin.

A decision on whether an autopsy should be carried out on Litvinenko won't be made until tomorrow at the earliest, because the coroner is waiting to hear from the Health Protection Agency on whether it is safe to perform the procedure, Cornish said.

Irradiation

Polonium 210 ``can only represent a radiation hazard if it is taken into the body -- by breathing it in, by taking it into the mouth, or if it gets into a wound,'' the agency said two days ago. ``It is not a radiological hazard as long as it remains outside the body.''

Polonium-210 is a radioactive substance that is found in the environment and in people at ``very low concentrations'' according to the Health Protection Agency. Litvinenko was found to have a ``significant quantity'' of the isotope in his body, it said. The U.K's National Health Service, referring to the former spy, said the substance had ``irradiated the patient severely.''

The isotope is also used for industrial purposes, and is found in anti-static devices used in factories, according to the agency. It has a half-life, the time period in which the concentration of radioactive particles halves, of 138 days, and emits harmful alpha particles when it decays.

Home Secretary John Reid told lawmakers he has chaired so- called COBRA meetings of government and health officials to discuss issues related to Litvinenko's death and the threat posed to the public by radiation from Polonium-210.

Russia

Police are investigating what they regard as a ``suspicious'' death, and they have not ruled out or ruled in any particular cause, Reid said, referring to the potential involvement of Russian authorities in the former spy's death.

``They should be ready to offer all necessary cooperation to the investigation as it proceeds,'' Reid said of the Russians.

Tom Kelly, a spokesman for Prime Minister Tony Blair, said today the Russian ambassador was summoned to the U.K. Foreign Office on Friday where he was asked if the embassy had any relevant information on Litvinenko. Blair hasn't spoken to Putin since the former spy died.

``We have to proceed carefully, there is a police enquiry on going,'' Kelly told reporters today at Downing Street. ``It's premature to be drawing any conclusions at this stage.''

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: November 27, 2006 11:18 EST