Former British health minister Wes Streeting says he would back Andy Burnham to replace Keir Starmer as prime minister, taking himself out of the contest and bolstering Burnham's position as frontrunner.
Starmer announced his resignation earlier on Monday.
Streeting, who quit Starmer's government in protest in May, had previously said he would take part in any contest to become prime minister.
But he threw his weight behind Burnham in a letter posted on X on Monday, saying the pair had spoken at length in recent days.
Streeting said he was convinced there was a place for his ideas on "progressive capitalism" under Burnham.
"We could spend the summer exaggerating small differences, or we can roll up our sleeves and help him to deliver the change our party and our country needs," Streeting said in his letter.
Nominations for Starmer's replacement as leader of the Labour Party will open on July 9, close by mid-July, and if there is a contest, a new leader will be in place by September.