Tony Blair says he agrees with Nigel Farage that the only way Leave campaigners can get the Brexit they want is to exit the European Union without a deal.
Brexit Party leader Mr Farage wants what he dubs a "clean break" from Europe in order to pursue a future outside of interference from Brussels.
And former Labour prime minister Mr Blair has used a radio interview to back up that point of view – but warned there would be a "huge amount of economic problems" if the UK did pursue a no-deal Brexit.
Boris Johnson successfully negotiated a Withdrawal Agreement with the EU last week but made a number of concessions to do so, including agreeing to checks on some goods entering Northern Ireland from Great Britain.
Mr Blair, who was in power for a decade after his 1997 landslide election victory, said the Prime Minister "sold out unionism" in order to agree a deal after being "bolt(ed) down" by Brussels.
"Bizarrely, though I profoundly disagree with him on whether Brexit is a good idea, actually Nigel Farage has actually produced one of the better analyses of what the problem is with Boris Johnson's deal," he said in a pre-recorded interview, due to air on talkRADIO on Sunday at 12pm.
"The problem in the end is if you really want to diverge on tax and regulation and go your own way on issues to do with trade, if you really want that the only way you're going to get that is by doing no-deal.
"If you do a deal with Europe they're going to bolt you down as we've just seen in relation to Northern Ireland."
Mr Blair said a fresh referendum, which he supports, should ask the public whether they want no-deal or to Remain an EU member.
"Ultimately, the question for the British people is do you want to do that no-deal Brexit with all, I would say, the huge amount of economic problems and difficulties that's going to happen, or do you want to stay. That is the actual choice," he told presenter Gavin Esler.
The three-time election winner said Labour should not approve Boris Johnson's request for a general election.
Mr Johnson said MPs could have more time to debate his Brexit deal in exchange for their support for a winter election on December 12.
Jeremy Corbyn, leader of the opposition, said Labour would wait to see the result of the EU's decision regarding the length of the Article 50 extension before clarifying its position.
European diplomats have postponed the decision regarding a delay until early next week but have said conversations will continue over the weekend.
Mr Blair said Labour could not trust Mr Johnson not to push through a no-deal Brexit and should withhold permission for an election while the PM is void of a majority.
"That's the core reason why, in my view, the Labour Party should not allow an election until he gives a definitive answer on the question of whether there's going to be a no-deal outcome," he added.
The New Labour pioneer said he still "always voted Labour" but admitted it was "a struggle" because of his "profound disagreement with the Corbyn leadership".