London: Former British prime minister Tony Blair has urged Britons to "rise up" and demand a second opportunity to vote on remaining in the European Union.
Mr Blair also took a swipe at Labour leader Jeremy Corbyn, saying the "debilitated" opposition party "facilitated" Brexit.
Pro-Brexit campaigners immediately condemned the intervention, with Foreign Secretary Boris Johnson urging voters to rise up and turn their TVs off when Mr Blair came on.
Speaking at Bloomberg's headquarters in London's financial district, where former Tory prime minister David Cameron announced the EU referendum five years ago, the former Labour leader said he was creating a new political movement to coalesce Remain activists to promote globalisation and stop Britain hurtling towards "Brexit at any cost".
Mr Blair said while he accepted the seismic result of last year's referendum, he contended: "But the people voted without knowledge of the true terms of Brexit."
He warned that Brexit could lead the break-up of the United Kingdom with Britain's decision to leave Europe's single trading market lending credibility to Scotland's continued push to hold a second referendum on independence.
Mr Blair said voters were entitled a second say "as these terms become clear" and said it was up to the left to persuade the nation to change its mind and stay in the EU. He said the Labour party, led by Mr Corbyn, was partly to blame for Remain's loss.
"The debilitation of the Labour Party is the facilitator of Brexit. I hate to say that, but it is true," he said.
Mr Corbyn was a lukewarm campaigner for Remain and was repeatedly accused of being secretly in support of Leave. Fairfax Media has contacted Mr Corbyn's office for comment.
Mr Blair is establishing a new political institution to promote globalisation and try and grow momentum for a second say on EU membership. However he ruled out a political comeback.
"This is not the time for retreat, indifference or despair, but the time to rise up in defence of what we believe – calmly, patiently, winning the argument by the force of argument but without fear and with the conviction we act in the true interests of Britain," he said.
Mr Blair was warmly received by supporters and members of Open Britain, an organisation campaigning to keep Britain "open and inclusive".
Prominent pro-Brexit campaigners condemned Mr Blair's speech and said it patronised the British people's decision to vote to leave.
Mr Johnson said Mr Blair had no credibility, having taken Britain into the Iraq war and advocating to join the eurozone.
"I urge the British people to rise up against and turn off the TV next time Blair comes on with his condescending campaign," he told the BBC.
Tory MP Andrew Rosindell, who campaigned for Brexit, told Fairfax Media Mr Blair was stuck in a time warp.
"Tony Blair needs to do us all a favour and stop grandstanding and patronising the British people – it's so 1997," Mr Rosindell said.
"Brexit will work and it's time for 'remoaners' like Blair to accept the democratic result. Blair and the Open Britain campaign need to realise that Brexit is going to be a success and the people are on side."
Former UKIP Leader Nigel Farage described Mr Blair as "yesterday's man".
But Scotland's First Minister Nicola Sturgeon praised Mr Blair's speech.
"Not his biggest fan, but there's a quality of analysis & argument in Blair's speech today that has been totally lacking from Labour to date," the SNP leader tweeted.
Mr Blair's intervention also divided Labour MPs.
Blair is right. Brexit won't deal w underlying challenges facing UK which drove Leave vote. Our duty is to give answers not ride the anger.— Liz Kendall (@leicesterliz) February 17, 2017
Tony Blair seems to feel economic & political institution that is the EU is perfect & Referendum shouldn't count. Labour right to disagree.— Richard Burgon MP (@RichardBurgon) February 17, 2017
Blair was one of most able political communicators of his age. As PM, mostly right. But several times, his judgment = direst consequences.— Richard Burgon MP (@RichardBurgon) February 17, 2017