LONDON - Nigel Farage, the leader of Britain's anti-EU UK Independence Party, said Prime Minister David Cameron had to step down after his campaign for Britain to stay in the European Union was defeated."I think we need to have a Brexit Prime Minister," Farage told ITV News."It's not acceptable, I don't think, for the serving backbenchers, for this man to stay on."The next Prime Minister should be one of the prominent Conservative "Leave" campaigners, he added."That competition could be between Michael Gove, Boris Johnson, Liam Fox, I don't know," he said.