A sitting UK prime minister has stepped down after his own party turned against him, deepening Britain's long run of political instability.

• Keir Starmer is resigning as Labour leader after his own MPs signaled they no longer want him leading them into the next election.
• He is the seventh UK prime minister in 10 years, a sign of how unstable British politics has become.
• He has told the King and asked his party to start picking a new leader, with the contest running through early-to-mid July.
• The handover leaves Labour without clear leadership for weeks while it sorts out who takes over.

Outlook: Labour will run a leadership race over the coming weeks, and whoever wins inherits a divided party and pressure to call a general election.