Alastair Campbell has declared he won't stay in Labour - even if he's readmitted - in a 3,000 word assault on Jeremy Corbyn .
Tony Blair's former spin chief branded Labour "asleep on the job" and said Mr Corbyn "has not led" on Brexit or anti-Semitism in a blistering attack today.
He said the party has been "taken over" by "Stalinists" - and claimed they are now crashing it towards a "very dark, dangerous place with an unbelievably right-wing, populist Government".
Mr Campbell hit out in BBC interviews and a lengthy screed in the New European, where he is an editor-at-large.
"I no longer wish to stay in the party, even if I should be successful in my appeal or legal challenge," he said.
"I hope that one day I will rejoin a party that genuinely appeals to the many not the few."
It comes after Mr Campbell for saying he voted Lib Dem in May's European elections.
His "automatic exclusion" - which he previously vowed to fight - prompted a backlash from ideological allies in Labour. And it triggered admissions by a string of grandees that they voted Lib Dem too.
It's understood Cherie Blair - the wife of former PM Tony - was among those who failed to back Labour in May's EU elections.
At the time Jeremy Corbyn suggested Mr Campbell should pledge loyalty to regain his membership, saying: "I look forward to his support for Labour in the future."
But in an all-out attack today Mr Campbell addressed his criticisms directly to the Labour leader.
He wrote: "Your half-hearted approach to the referendum campaign three years ago had a role in Leave winning.
"Your failure to provide consistent leadership on the issue since then has been a huge disappointment.
"Your failure to challenge the lies, crimes and misdemeanours of the Leave campaign; your pursuit of Labour versions of unicorns, such as a 'jobs first Brexit,'; your failure to master the detail sufficient to provide confidence to the public, or indeed to Europe, that you would be able to negotiate a better deal; your refusal, despite having become leader in large part by promising to listen to members, to do so on Brexit; your failure to mount the democratic case for the public having the right to say, given all we now know, whether they wish to proceed - these have all played into the hands of our opponents."
Jeremy Corbyn has announced Labour will support a second referendum on any Brexit deal after months of internal wrangling.
However, Labour could still go into the next general election vowing to get a Brexit deal with the EU, which would then be put to a public vote.
Mr Campbell told BBC Radio 4's Today programme: "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."
Mr Campbell said new Prime Minister Boris Johnson is trying to "clear the decks towards a general election" by heaping blame for Brexit failure on Parliament and the civil service.
"He thinks, probably rightly, that the country's decided they will not put Jeremy Corbyn into office and I think we have to face up to that truth," he said.
He added: "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."
Asked if he would be joining the Lib Dems, Mr Campbell said: "No, I don't feel I'm close to other parties.
"But I do think if we do get to a general election and the choice facing the country is Boris Johnson or Jeremy Corbyn all sorts of things are going to happen because that is not a choice that this country finds remotely palatable."
Responding to Mr Campbell's attack, Labour shadow minister Danielle Rowley told the BBC: "The Labour Party has always been and remains a broad church.
"I'd like it if he could get on board but it seems he really doesn't want to do that.
"If he is really interested in making sure the Labour Party is doing what he thinks it should be doing, why is he not having these conversations privately and trying to genuinely talk about his concerns?
"Rather than going out and writing letters in the papers and doing it publicly? I think that's really disappointing."
