Authorities found traces of radiation on two British Airways jetliners in London, grounded a third plane in Moscow, and asked passengers on more than 200 flights to come forward as investigators widened their search for clues in the poisoning death of former Russian spy Alexander Litvinenko. All three planes had been on the London-Moscow route, British Airways said. In the last three weeks the planes had also traveled to routes across Europe, including Barcelona, Frankfurt and Athens. Around 30,000 passengers had traveled on 220 flights on those planes, said Kate Gay, a spokeswoman for the airline. It said it had been told the risk to the public was low.