Alastair Campbell says he no longer wants to be a Labour member, claiming the party is facing an “existential crisis” due to poor leadership.
Tony Blair’s former spin doctor had been set to challenge the party’s decision to kick him out after he voted Lib Dem in May’s EU elections.
But in an open letter to Jeremy Corbyn, he said he did not want to return.
He said Labour had been “taken over” and it was “time to stop pretending” it was the party it used to be.
Mr Campbell told BBC Radio 4’s Today programme Mr Corbyn “has not led on Brexit” or “the anti-Semitism issue”, and the leadership “kid themselves that there’s a policy agenda that the country out there is even aware of”.
“What you have to do in opposition to win against a ruthless Tory Party, you have to do far more that is being done now. And we have to be honest about that.”
He said he feared Prime Minister Boris Johnson was trying to “clear the decks towards a general election” because he believed the Labour leader’s “weakness” made a Conservative victory more likely.
“He thinks, probably rightly, that the country has decided it will not put Jeremy Corbyn into office,” Mr Campbell continued.
“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 whether he would join the Liberal Democrats, he said he was not “close to other parties” and had not yet decided who to vote for at the next election.
In his open letter, he said he hoped to one day rejoin a party “that genuinely appeals to the many not the few”.
Labour said at the time his expulsion was “automatic” because he had admitted voting for another party.
Who is Alastair Campbell?
Mr Campbell was a political journalist before coming to prominence in Whitehall as a key member of the Labour PM’s staff in 1994.
He served as Mr Blair’s chief press secretary until 2000 and was a controversial figure, heavily involved in policy, including over the Iraq War.
Since leaving government, he has opened up about his struggles with depression and alcoholism, and works with a number of charities.
He also campaigns for the People’s Vote and is editor-at-large of The New European magazine.