John Reid told parliament that police are monitoring 24 sites and have found radiation in 12 of them, but said the health risk to the public is very low.
Alexander Litvinenko, a Russian security defector and a close associate of fugitive Russian oligarch Boris Berezovsky, died last Thursday in a London hospital. British health officials said Friday a large dose of radioactive polonium-210 had been found in his body.
Five planes that flew the Moscow-London route have been singled out for radiation tests as part of investigations. So far two British Airways jets grounded in London have tested positive for radiation contamination.
British Airways said the planes being tested made a total of 221 flights in Europe between October 25 and November 29.
Airline officials said the company had been trying to contact and advise all 33,000 passengers who traveled on the planes from October 25, a week before Litvinenko claimed to have been poisoned in a London sushi bar.
