The British government appealed for calm on Monday as scientists discovered more traces of radiation and three people who fell sick were being tested for the deadly radioactive poison that killed former Russian spy Alexander Litvinenko. The government ordered a formal inquest into his death and Home Secretary John Reid, in a special address to the House of Commons, warned against rushing to conclusions over who might be responsible for the 43-year-old former KGB agent turned Kremlin critic, who died after falling ill from what doctors said was polonium-210 poisoning. The substance is deadly if ingested or inhaled. Reid said the tests on the three people were only a precaution. High doses of polonium-210 -_ a rare radioactive element usually manufactured in specialized nuclear facilities - were found in Litvinenko's body. "The nature of this radiation is such that it does not travel over long distances, a few centimetres at most, and therefore there is no need for public alarm," Reid said in a special address to the House of Commons after opposition calls.