From Fox News:

Britain’s Prime Minister Keir Starmer announced Monday that he will resign following a mounting revolt inside the Labour Party after devastating local election losses, the resignation of government ministers and growing pressure from senior members of his own cabinet. Starmer said he would step down as prime minister and Labour leader after concluding he could no longer unite the party, but is expected to remain in office until a successor is chosen.
“Every decision I’ve taken has been about putting the country I love first. That is why I will resign as leader of the Labour Party. I have spoken to his majesty the king this morning to inform him of my decision,” he said while delivering a statement outside of 10 Downing Street.