Radioactive traces of the substance that poisoned former KGB agent Alexander Litvinenko have been found aboard at least two planes of the British Airways, the company announced. The airline is making contact with up to 33,000 passengers after traces of polonium-210 were found on two Boeing 767 aircraft grounded at Heathrow airport in London, while a third plane is being probed in Moscow. Up to 33,000 passengers travelled on the 221 European flights affected, including 33 on the London to Moscow route, BA said. Barcelona, Dusseldorf, Athens, Stockholm, Vienna, Frankfurt, Madrid and Istanbul were among the destinations to which flew radiation-affected planes. Earlier in the week traces of radiation were found at several addresses, including the London hotel and a sushi bar the Russian ex-spy visited on November 1. The traces of polonium-210 were also found at a building in Grosvenor Street, Mayfair, and an office block in Down Street, west London. Home Secretary John Reid told MPs that Russia had been asked to co-operate in the inquiry into Litvinenko's death. In an emergency statement in the Commons on Monday, Reid said the Russian ambassador had been called to the Foreign Office at the end of last week. The death of the 43-year-old former KGB colonel last Thursday has been linked to the discovery of polonium-210 in his body.