Alastair Campbell has said he "no longer" wants to be part of the Labour Party under Jeremy Corbyn.
The former director of communications during Tony Blair's time as Prime Minister was expelled from the party in May after admitting voting for the Liberal Democrats in the European elections.
He had planned to appeal, but speaking to talkRADIO's Julia Hartley Brewer, he was reconsidering which party to pledge his support to.
“I’m not following Chuka Umunna to the Lib Dems, I’m not part of Change. I’m gonna take my time and think about it,” he said.
“But I know that what we have at the moment is utterly unsustainable and I know that this Labour Party is not the Labour Party that I’ve dedicated my life to.”
The campaigner for a second referendum said the “communists and Stalinists” in Labour must “stop pretending” Jeremy Corbyn is the man who can lead the party back into power.
“I’m not one of those people who thinks they should all rise-up against Jeremy Corbyn because they’ve tried that and it didn’t work,” he said.
“There comes a point, surely, where somebody who is in that position of leadership has to look deep into themselves and say ‘can I do this job? Can I rise to this challenge?’”
Mr Campbell wrote an open letter to Jeremy Corbyn in which he accused the Labour leader of failing to grasp the seriousness of the political climate.
"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 wrote.
Last week, Mr Corbyn said Labour will "campaign to Remain" if Prime Minister Boris Johnson puts an unsatisfactory Brexit deal back to the public in a second referendum.
"Labour will oppose any deal that fails to protect jobs, workers' rights or environmental protections. If you have the confidence to put that decision back to the people, we would, in those circumstances, campaign to Remain," he said.