The resumption of US strikes against Iran has thrust incoming UK Prime Minister Andy Burnham into a potential day one decision on how much to support Britain’s closest ally in its controversial military campaign. Even as Burnham was installed as leader of the governing Labour Party on Friday, outgoing Prime Minister Keir Starmer’s government was engaged in high-level talks about renewed US attacks on Iran, according to people familiar with the matter. The prime minister-in-waiting was kept...