The likely next U.K. prime minister has chosen one of his oldest political allies in Westminster who helped him become an MP in 2001.

The embattled British prime minister is widely expected to announce a plan for his exit just as his likely successor, Andy Burnham, arrives in Westminster.

The transition period includes a high-stakes NATO summit. One key EU meeting has already been postponed.

Andy Burnham is poised to become Britain's next prime minister unopposed as potential rival Darren Jones declared he won't run. Meanwhile, outgoing leader Keir Starmer, seeking to…