Britain said it had summoned the Russian ambassador to London on Thursday after Russian bombers were found flying close to British airspace, saying the incident had disrupted civil aviation. The move comes after a string of similar incidents and amid tense relations with Moscow over the conflict in Ukraine and a London inquiry into the poisoning of former Russian spy Alexander Litvinenko. The Ministry of Defence said such incursions by Russian planes were currently running at around one a month and that the latest happened off the south coast of England.