(Reuters) - European stock markets dived almost 3% to log their worst day since last December on Wednesday as the threat of a transatlantic trade war and dismal economic data added to fears about a faltering global economy. Losses in London were the most dramatic, with the FTSE 100 seeing its worst session in 3-1/2 years after Prime Minister Boris Johnson unveiled a final Brexit proposal that dimmed the chances of Britain leaving the European Union with a deal. [.L]In Europe, Airbus dropped..