Tony Blair’s former director of communications Alastair Campbell has said he no longer wants to be a Labour member, as he warned the party under Jeremy Corbyn‘s leadership faced an “existential crisis”.

In an open letter to the Labour leader, the former No 10 spin doctor claimed Mr Corbyn is unlikely to win a majority if a general election is called in the coming months.

Insisting Labour could be “destroyed as a serious political force”, Mr Campbell made clear he does not want to rejoin the party. He was expelled in May after saying he had voted for the Liberal Democrats at the European elections in protest at Labour’s stance on Brexit.

In his letter to Mr Corbyn, published today, he wrote: ”With some sadness but absolute certainty, I have reached the conclusion that I no longer wish to stay in the party, even if I should be successful in my appeal or legal challenge.”

The longstanding critic of Mr Corbyn said the party had been “taken over” by Stalinists and Communists, adding: “Let’s stop pretending this is the Labour Party we really believe in.”

Boris Johnson's cabinet: Who's in and who's out Show all 40 1 /40 Boris Johnson's cabinet: Who's in and who's out Boris Johnson's cabinet: Who's in and who's out In: Jacob Rees-Mogg Jacob Rees Mogg appointed Leader of the Commons AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Esther McVey Esther McVey appointed housing secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Jo Johnson Jo Johnson appointed new business and energy secretary EPA Boris Johnson's cabinet: Who's in and who's out In: Brandon Lewis Brandon Lewis appointed immigration secretary Getty Boris Johnson's cabinet: Who's in and who's out In: James Cleverly James Cleverly appointed Conservative Party chairman PA Boris Johnson's cabinet: Who's in and who's out In: Baroness Evans Baroness Evans remains Leader of Lords PA Boris Johnson's cabinet: Who's in and who's out In: Julian Smith Julian Smith appointed Northern Irish secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Alister Jack Alister jack appointed Scottish secretary PA Boris Johnson's cabinet: Who's in and who's out In: Alun Cairns Alun Cairns remains Welsh secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Grant Shapps Grant Shapps appointed transport secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Alok Sharma Alok Sharma appointed international development secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Robert Buckland Robert Buckland appointed justice secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Amber Rudd Amber Rudd remains work and pensions secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Robert Jenrick Robert Jenrick appointed housing and communities secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Andrea Leadsom Andrea Leadsom appointed business secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Nicky Morgan Nicky Morgan appointed culture secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Gavin Williamson Gavin Williamson appointed education secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Theresa Villiers Theresa Villiers appointed environment secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Liz Truss Liz Truss is appointed international trade secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Ben Wallace Ben Wallace appointed defence secretary EPA Boris Johnson's cabinet: Who's in and who's out In: Stephen Barclay Stephen Barclay remains EU secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Dominic Raab Dominic Raab appointed foreign secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Priti Patel Priti Patel appointed home secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Michael Gove Michael Gove given Chandellor of the Duchy of Lancaster AFP Boris Johnson's cabinet: Who's in and who's out In: Sajid Javid Sajid Javid is appointed Chancellor of the Exchequer AP Boris Johnson's cabinet: Who's in and who's out Out: Jeremy Hunt Jeremy Hunt sacked as foreign secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Matt Hancock Matt Hancock remains health secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out Out: Chris Grayling Chris Grayling resigned as transport secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: Jeremy Wright Jeremy Wright sacked as culture secretary PA Boris Johnson's cabinet: Who's in and who's out Out: Karen Bradley Karen Bradley sacked as Northern Ireland secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: James Brokenshire James Brokenshire sacked as housing and communities secretary Reuters Boris Johnson's cabinet: Who's in and who's out Out: Penny Mordaunt Penny Mourdaunt sacked as defence secretary Reuters Boris Johnson's cabinet: Who's in and who's out Out: Liam Fox Liam Fox sacked as international trade secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: Greg Clarke Greg Clarke sacked as business secretary PA Boris Johnson's cabinet: Who's in and who's out Out: David Mundell David Mundell sacked as Scottish secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: Damien Hinds Damien Hinds sacked as education secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: David Gauke David Gauke resigned as justice secretary EPA Boris Johnson's cabinet: Who's in and who's out Out: Rory Stewart Rory Stewart resigned as international development secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: David Lidlington David Lidlington resigned as deputy Prime Minister PA Boris Johnson's cabinet: Who's in and who's out Out: Philip Hammond Philip Hammond resigned as Chancellor of the Exchequer AFP/Getty

Mr Campbell, also a supporter of a Final Say referendum, continued in his letter: “The culture you have helped to create has made the party one that I feel no longer truly represents my values, or the hopes I have for Britain.”

He said he does not blame Mr Corbyn for Brexit, something he ascribed to successive recent Conservative prime ministers and senior Tories, but he said the Labour leader does not understand the gravity of the UK’s situation.

“I see no sign that you and your office have grasped the seriousness of what is happening, let alone devised or begun to execute a strategy to respond and defeat it,” Mr Campbell wrote.

Speaking about his decision on BBC Radio 4’s Today programme, Mr Campbell also insisted Labour and Jeremy Corbyn are ”asleep on the job”.

“This isn’t about being spiteful,” he added. “I think that with Jeremy Corbyn he has got to look deep into himself and say is he up to the job, is he up to the challenge that [he] now faces because if not, we are heading to a very dark, dangerous place with an unbelievably right-wing, populist government and the answer to which is not a populism of the left.”

He continued: “I don’t think it’s personal, I think I’m saying what I think, it’s based on a lot of experience of campaigns and of politics, and reading it as I read it now, Labour is facing its own existential crisis... I think there is a danger that we’re going to be destroyed as a serious credible political force unless we face up to the reality of what’s going on.”

On Labour’s Brexit policy, Mr Corbyn reiterated at the weekend his support for a referendum on any deal reached with the European Union, and said even if Labour is in government a public vote would be held.

He refused, however, to say whether Labour would back Remain or its own negotiated deal if the party came to power.