The big question facing ​A​ndy Burnham is not whether Brexit has harmed Britain, but if a rapidly changing Europe will keep the door open​ if the UK decides it wants back in • Don’t get This Is Europe delivered to your inbox? Sign up here It was lobbed into the national conversation without fanfare or warning, almost a footnote in the UK prime minister’s first speech as leader to his governing Labour party’s annual conference. But Andy Burnham has kicked off a quiet U-turn on Brexit. By stating bluntly that the decision to leave Europe’s core political community had done “more harm than…