Sadiq Khan has weighed in on the race to replace Jeremey Corbyn as the Leader of the Labour Party, endorsing Sir Kier Starmer, who Khan says is the “best person to unite” the party.

The leftist mayor of London announced on Twitter that he will be voting for the shadow Brexit secretary, passing over MP for Wigan Lisa Nandy and the ‘continuity Corbyn’ candidate Rebecca Long-Bailey.

“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,” Khan wrote.

In response to the endorsement, Sir Kier 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.”

The anti-Brexit MP for Holborn and St Pancras is seen as more moderate than his rivals, however, during the 1980s, Starmer helped establish a Marxist journal called Socialist Alternatives. The magazine called for a “radical extension of common ownership over wealth and power” and in one editorial said that “prisoners should have much greater control over the conditions of their own imprisonment”, according to The Times.

Sir Kier is widely considered the frontrunner in the leadership race, with the latest odds by bookmakers putting his chances of winning at 89 per cent.

The endorsement from Mr Kahn comes one day after the Labour Party sent an email to members from shadow chancellor and Corbyn ally, John Mcdonnel, urging them to vote for Rebecca Long-Bailey, despite the party’s policy of not making any official endorsements in the leadership race.

McDonnel called Long-Bailey a “working-class woman” that would “carry forward our socialist programme”, according to The Telegraph.

The email sparked a row over perceived bias in the party and rival candidate Lisa Nandy is planning to lodge an official complaint with the party over the incident, with one source saying that it was a “clear breach of the rules”.

Ms Nandy, once seen as a longshot to get the leadership nod, has surged in the rankings, with bookies putting her chances at winning the race at sixteen to one, compared to thirty-three to one earlier in the week.

Membership voting in the leadership race began on Monday and members will have until April 2 to cast their ballots, with the next leader to be announced on April 4.

Follow Kurt on Twitter at @KurtZindulka