Morgan McSweeney, a behind-the-scenes strategist, has emerged as the most powerful unelected figure in Britain, credited with transforming the Labour Party by purging its hard-Left elements. His influence is so extensive that even senior Cabinet ministers and Chancellor Rachel Reeves defer to his judgment, with the phrase 'What does Morgan think' dominating discussions at Number 10. McSweeney's journey from a restless youth in Ireland to Labour's chief of staff is marked by his tactical prowess in local politics and his role in orchestrating Labour's landslide victory, as well as shaping the Starmer Cabinet.

He played a pivotal role in securing Peter Mandelson's controversial appointment as ambassador to Washington, despite opposition from security services and Cabinet members. McSweeney's strategic moves also ensured rapid advancement for his wife, Imogen Walker, within the party, and he was instrumental in rewriting Labour's rulebook to prevent the hard-Left from regaining influence. His discreet yet decisive presence was highlighted when he was photographed alongside Starmer at the White House, celebrating Mandelson's appointment—a move that ultimately proved to be a costly error for the party leadership.