The former Labour Prime Minister, who has previously said Britain should “keep its options open” over a second referendum, signalled his determination to re-engage in British politics.
He said he believed he could not return to the frontline because of media hostility, but intended to play a significant role behind the scenes.
Mr Blair, a strong supporter of EU membership, insisted the Brexit process could be halted, outlining two scenarios under which that could happen.
“It can be stopped if the British people decide that, having seen what it means, the pain-gain cost-benefit analysis doesn’t stack up.
And that can happen in one of two ways. I’m not saying it will [be stopped], by the way, but it could,” he told New Statesman.
Mr Blair said the crucial factor would be the deal which Theresa May reaches over regaining control over EU migrants.
“Either you get maximum access to the single market – in which case you’ll end up accepting a significant number of the rules on immigration, on payment into the budget, on the European Court’s jurisdiction.
“People may then say, ‘Well, hang on, why are we leaving then?’
“Or alternatively, you’ll be out of the single market and the economic pain may be very great, because beyond doubt if you do that you’ll have years, maybe a decade, of economic restructuring.”
He added: “This is like agreeing to a house swap without having seen the other house . . . You’ve got to understand, this has been driven essentially ideologically.”
NO RETURN TO FRONTLINE
Following speculation he was planning a comeback, Mr Blair said he wanted to work to revive the “progressive centre or centre left” and give a voice to millions of people who feel disenfranchised.
He said: “I can’t come into frontline politics. There’s just too much hostility, and also there are elements of the media who would literally move to destroy mode if I tried.”
The former Prime Minister said was trying to create space for a debate over the future of progressive politics.
“I’m dismayed by the state of Western politics, but also incredibly motivated by it. I think, in Britain today, you’ve got millions of effectively politically homeless people.”
Labour’s former leader said the party had been “captured” by the far left but denied calling Jeremy Corbyn a “nutter”.
“I just think he is someone on the far left of politics and he’s been consistent for the last 35 years that I’ve known him, which is fine.”
Asked whether Mrs May agreed that Brexit could be stopped, her spokeswoman replied: “The PM has been very clear we are leaving the EU.
“That was the decision of the British people. There is not going to be any change from that position.”
• This article was first published on our sister website inews.co.uk