Sadiq Khan has backed Keir Starmer to be the next leader of the Labour party.
The endorsement, which comes the weeks voting opens in the contest, sees Labour's most senior elected politician throw his weight behind Sir Keir's bid to replace Jeremy Corbyn .
In his tweet announcing his support the London Mayor said: "I will be voting for @Keir_Starmer to be the next Labour leader.
"I've known Keir for decades. He's the best person to unite our party, take the fight to the Tories and put Labour in government."
After recieving the endorsement Sir Keir said: "I’m honoured to have received Sadiq’s backing to be the next Labour leader.
"Sadiq is demonstrating that Labour in power can change lives. I look forward to campaigning alongside him to keep London Labour."
Sir Keir is the clear frontrunner in the leadership contest.
He won more than double the amount of CLP support than second-placed Ms Long-Bailey and is the bookies' favourite.
He also performed the strongest in winning the support of unions and affiliated socialist organisations.
Around 600,000 people start being sent ballots this week in the Labour leadership contest.
The race runs for more than 40 days despite starting back in early January - and the winner will take office on April 4.
Either Keir Starmer, Rebecca Long-Bailey or Lisa Nandy will then replace Jeremy Corbyn immediately and be charged with cleaning up Labour's worst election defeat since 1935.
Members, affiliates and registered supporters can begin casting their ballots today to choose the person to take the party forward against the Tories.
