Labour could swing Brexit battle for Cameron

By William James WOLVERHAMPTON (Reuters) - The prime minister's battle to keep his country in the European Union - and save his political future - may depend on the campaigning power of his fiercest rivals: the opposition Labour Party. On June 23 Britain will vote on whether to withdraw from the EU in a referendum that has scrambled the traditional left-right battle lines of British politics. Cameron has staked his political legacy on being able to persuade Britons to stay inside the 28-member b