U.K. Prime Minister Sir Keir Starmer attends an opening session on the first day of the Labour Party conference at ACC Liverpool on September 28, 2025 in Liverpool, England. Dan Kitwood | Getty Images News | Getty Images U.K. Prime Minister Keir Starmer's leadership is hanging by a thread as a growing number of his own party's lawmakers call on the Labour Party leader to resign. The move against Starmer comes after the ruling Labour Party performed badly in local elections last week, losing votes to parties on both the left and right of the political spectrum. CNBC has a brief guide to what's going on and what could happen next in the U.K. What is going on? Starmer's premiership is on a knife-edge this week as a significant number of Labour Party MPs have openly mutinied, calling for the PM to resign immediately, or to set out a timetable for his departure.…