Defying Cameron, London's mayor to campaign for British exit from EU

By William James and Guy Faulconbridge LONDON (Reuters) - London Mayor Boris Johnson on Sunday threw his weight behind the campaign to leave the European Union, dealing a blow to David Cameron by increasing the chance British voters will ditch membership in a June referendum. In a move that electrified the referendum campaign by pitting one of Britain's most charismatic politicians against the prime minister, Johnson said Cameron had failed to deliver fundamental reform with an EU deal struck on