Defying Cameron, London Mayor Boris to campaign for British exit from EU

By William James LONDON (Reuters) - London Mayor Boris Johnson said on Sunday he backed leaving the European Union, dealing a blow to Prime Minister David Cameron by giving the "out" campaign a de facto leader who is one of the most charismatic politicians in British politics. Forty-three years after Britain joined the EU's predecessor, Cameron announced a June 23 referendum on Saturday after clinching a deal from 27 other leaders to give Britain what he said was a special status.