UK advises 48 countries on polonium tests

London - Britain is working with nearly 50 countries to help them assess the risk to 450 people who fear they may have been exposed to the radioactive poison that killed former Russian agent Alexander Litvinenko in London.

The Health Protection Agency (HPA) said on Thursday that tests in Britain alone had identified 116 people who had "probable contact" with the poison, Polonium 210, but only 13 of these showed levels that required further monitoring.

The 13, mostly London hotel staff, were assessed to have received radiation doses above six millisieverts (mSv), but the dose that killed Litvinenko was "many thousands of times greater", HPA chief executive Pat Troop said.

The risk of a fatal cancer is 0.005 percent per mSV, so 6 mSV equates to a risk of 0.03 percent - tiny when considered that the general population has a 23 percent chance of dying from cancer anyway.

Troop said the HPA was sharing its data and testing methods with dozens of countries whose nationals had visited sites including a London hotel and sushi bar, where Litvinenko held meetings on the day he fell ill.

"We've been working with 48 other countries who have between them around 450 of their nationals who were affected through this incident," she told a news conference.

"We've been sending them a lot of information ... about how they might assess their risk."

Litvinenko, a former FSB security agent who became a fierce critic of the Kremlin in exile, died an agonising death in a London hospital and accused Russian President Vladimir Putin of ordering his death, a charge dismissed by Moscow.

Investigators subsequently discovered a trail of radiation across London at hotels, restaurants, bars, offices and even a soccer stadium visited by people who had dealings with him.

British police are investigating his death as murder and have visited Moscow to attend questioning of Litvinenko's Russian associates by authorities there.

It remains unclear how the 13 people with doses over six mSv absorbed the traces of polonium. HPA officials said hotel workers could, for example, have inhaled it in dust or ingested it by touching contaminated crockery and then eating something themselves without washing their hands.

An associate of Litvinenko, Yuri Shvets, told the BBC last month that he had drunk tea with two Russians on November 1 at the Pine Bar of the Millennium Hotel, where British tests show eight staff and two guests received doses above six mSv.

In addition, authorities in the Netherlands said last month that a Dutch guest who stayed at the same hotel had tested positive for a very low level of polonium.