The former prime minister said Mr Corbyn was an “existential threat” to the party, but said he still hoped that Labour is not “lost”.
Another leading figure of the Blair era, Lord Blunkett, warned the party is facing “irrelevance” unless there is a rethink of the “Corbyn project”.
But Mr Corbyn’s supporters hit back arguing that Mr Blair was “never in the right party” and that Labour was “more united than ever”.
Reports have emerged in recent weeks that a group of Labour MPs are planning to break away and sit as an independent group in the House of Commons.
Mr Blair told BBC Radio 4’s Today programme: “I’ve been a member of the Labour Party for over 40 years. You do feel a strong loyalty and attachment, but at the same time it’s a different party. The question is, can it be taken back?
“This is a different type of Labour Party. Can it be taken back? I don’t know.”
Mr Blair’s comments follow Frank Field’s resignation of the party whip over the antisemitism row and allegations of bullying among members.
The veteran MP, who served as welfare minister in Mr Blair’s cabinet, cited “a culture of intolerance, nastiness and intimidation” among his concerns.
Saying Mr Corbyn poses an “existential threat” to the party, Mr Blair added: “There’s lots of people associated with me who feel that the Labour Party’s lost, that the game’s over. I’m kind of hoping they’re not right.”
Lord Blunkett, a Labour MP for 28 years and a minister for most of Mr Blair’s administration, said he was not sure if he would back the party even if he knew his vote would make the difference between Mr Corbyn becoming prime minister or not.
Asked what he would do in these circumstances, the Labour peer said: “It would entirely depend on whether my good friends in the Parliamentary Labour Party and the Commons hadn’t been deselected and were there to ensure that the sane, rational policies of a Labour Party for the future were going to be implemented.”
But Mr Blair’s intervention sparked a backlash from Mr Corbyn’s supporters, with MP Chris Williamson saying he did not understand Mr Blair’s argument, given the huge support Mr Corbyn enjoyed in the party membership.
He said: “The Labour Party has never been more united. It is going from strength to strength.”
Jon Lansman, the founder of Corbyn-backing activist group Momentum, said: “Tony Blair was never in the right party and there will never be a return to his politics in [Labour]”
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