Former U.S. President Barack Obama called in at the British Prime Minister’s official residence on Monday, but the office is keeping tight-lipped about the purpose of the one-hour meeting. Barack Obama surprised when he turned up at Rishi Sunak’s front door on Monday, going inside the historic Downing Street residence for an hour and meeting with the Prime Minister. Former President Obama walked up to the famous black door alone but later emerged alongside the U.S. Ambassador to London Jane Hartley. Former US President Barack Obama has arrived at 10 Downing Street for a private meeting. pic.twitter.com/l9hZEHyYvp — Harry Stedman...