Sir Keir Starmer resigns as Prime Minister and also steps down as Labour Party leader, triggering a process to choose his successor. Multiple reports say Starmer announces that a Labour leadership contest will follow, with the party selecting a new leader who will then become prime minister. The process involves a leadership race to replace Starmer as Labour leader, and it sets the terms for when the new leader is chosen. While the specific timeline and procedural details are not fully laid out in the provided accounts, the overall sequence is consistent: Starmer resigns, Labour holds a contest to determine its next leader, and that outcome leads to a new prime minister. The reports therefore focus on what happens next in the transition, centring on Labour’s internal leadership arrangements and the resulting change in government leadership. No alternative mechanism is described in the sources beyond a party leadership contest linked directly to the next prime minister.