Jamie Driscoll, who was Labour's North of Tyne mayor, said he had "no other choice" but to quit the party after he was barred from running as North East mayor last month.

He said he would now serve the region as an independent mayor.

In a letter to the Labour leader, Mr Driscoll accused Sir Keir of breaking "so many promises", including plans to scrap tuition fees, watering down a £28bn commitment to tackle climate change and introducing universal free school meals.

He claimed the Labour leader told him in 2020 - when Sir Keir was running to lead the party - that "disciplining people to be united is going nowhere".

He wrote: "You've U-turned on so many promises: £28 billion to tackle the climate emergency, free school meals, ending university tuition fees, reversing NHS privatisation; in fact, a list of broken promises too long to repeat in this letter.

"It is not grown-up politics to say Britain is broken, and then claim things are now so difficult we will abandon any plan to fix it. That is mental gymnastics worthy of Olympic gold."

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Mr Driscoll added: "Worst of all, you've said you're not interested in hope and change.

"Well, I am - Britain needs hope and change. Instead of London Labour HQ barring me from running, you could have used my work as a showcase of economic competence."

The decision to bar Mr Driscoll from the longlist to be the next North East mayor - a role that was created as part of a £1.4bn devolution deal for the region - was immediately criticised by MPs on the left, including former shadow chancellor John McDonnell, who branded the news "staggering".

Clive Lewis, the Labour MP for Norwich South, said he was "shocked by such sectarian behaviour".

Sky News reported that Mr Driscoll's candidacy was refused because he recently appeared at an event with the film director Ken Loach, who was expelled from the party in 2021 for claiming there had been a "purge" and "witch hunt" of Jeremy Corbyn supporters under Sir Keir Starmer's leadership.

Asked about the controversy by Sophy Ridge on Sky News last month, Mr Driscoll refused to condemn controversial remarks made by Mr Loach about Jews, Israel and the Holocaust.

They include saying that Israel's actions made a rise in antisemitism understandable, and replying that "all history" was up for discussion when asked if the Holocaust was unacceptable or if Israel's founding was based on ethnic cleansing.

Mr Driscoll said this was a question for Mr Loach, and that he was "not a spokesman for Ken Loach".

"My combined authority has adopted the… IHRA [International Holocaust Remembrance Alliance] definition of antisemitism," he added.

"I've been on Jewish Labour Movement training, I work very closely with the Jewish Leadership Council... visit the synagogues in my region."

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In a final swipe at Sir Keir, Mr Driscoll said key figures in the region had encouraged him to run as an independent, "saying they will vote for me because the North East needs an autonomous voice that's not in hock to Westminster Party HQs".

A Labour spokesperson said: "The Labour Party is delighted that local party members have selected Kim McGuinness as our candidate for the North East Mayoral election next year.

"With Keir Starmer as leader, the Labour Party is a changed party, relentlessly focussed on delivering for working people, and we make no apologies that Labour candidates are held to the highest standard.

"The Tories have let our region down, and as Labour mayor, Kim will be the strong voice the North East deserves."