The former British PM is pushing for another referendum...
Tony Blair has been accused of "insulting the intelligence" of voters and "arrogance" after he urged opponents of Brexit to "rise up" against leaving the EU.
The former prime minister said voters backed severing ties with Brussels without knowing the true cost and should have the chance to change their minds.
In a speech in London, Mr Blair questioned whether the referendum had given a mandate for "Brexit at any cost".
But his intervention has drawn the ire of Brexit supporters, with British foreign secretary Boris Johnson accusing him of "insulting the intelligence" of those who voted to leave.
The leader of the official Vote Leave campaign in the referendum said: "I respectfully say to Tony Blair, those who call the British people to rise up against Brexit, I urge the British people to rise up and turn off the TV the next time Blair comes on with his condescending campaign."
Michael Gove, another prominent Leave campaigner, said: "Politicians like Tony Blair should respect the result and work with the Government to make a success of Brexit instead of trying to undermine British democracy."
In an impassioned speech, Mr Blair rejected the idea that leaving was now "inevitable", adding: "I accept right now there is no widespread appetite to re-think.
"But the people voted without knowledge of the true terms of Brexit. As these terms become clear, it is their right to change their mind. Our mission is to persuade them to do so.
"I don't know if we can succeed. But I do know we will suffer a rancorous verdict from future generations if we do not try.
"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."
Mr Blair said: "What was unfortunately only dim in our sight before the referendum is now in plain sight. The road we're going down is not simply 'hard Brexit', it is now 'Brexit at any cost'.
"Our challenge is to expose relentlessly what that cost is, to show how that decision was based on imperfect knowledge, which will now become informed knowledge, to calculate in easy to understand ways how proceeding will cause real damage to our country, and to build support to find a way out from the present rush over the cliff's edge."
Blair also warned that Brexit could lead to Scottish independence.
The 63-year-old's speech will be seen as a signal that he would like to create a new pro-Remain political party made up of Blairites, Liberal Democrats and even some pro-EU Conservatives.
Mr Blair has, however, put himself at odds with British Labour leader Jeremy Corbyn, who last week ordered the party's MPs to vote for the Government's Article 50 bill.
The Brexit secretary David Davis admitted this week that the British government is expecting amendments to be passed and predicted "ping pong" between the Commons and the Lords.
Blair made his speech to the Open Britain group, whose leading figures include the Liberal Democrat's Nick Clegg and Norman Lamb, Labour's Chuka Umunna and Pat McFadden, and Conservatives Anna Soubry and Dominic Grieve.
He continued: "How hideously, in this debate, is the mantle of patriotism abused. We do not argue for Britain in Europe because we are citizens of nowhere.
"We argue for it precisely because we are proud citizens of our country who believe that in the 21st century, we should maintain our partnership with the biggest political union and largest commercial market right on our doorstep; not in diminution of our national interest, but in satisfaction of it."
Declaring that immigration is driving the Brexit debate, Blair said: "There is in some parts of the country a genuine concern about numbers from Europe - real pressures on services and wages.
"But for many people, the core of the immigration question – and one which I fully accept is a substantial issue – is immigration from non-European countries, especially when from different cultures in which assimilation and potential security threats can be an issue.
"Nonetheless, we have moved in a few months from a debate about what sort of Brexit, involving a balanced consideration of all the different possibilities, to the primacy of one consideration – namely controlling immigration from the EU – without any real discussion as to why and when Brexit doesn't affect the immigration people most care about."
Mr Blair said that in the absence of an effective opposition, pro-Europeans need to build a "movement" that went beyond party lines.
He said the institute he was launching would play its part in developing the arguments to rethink Brexit: "The debilitation of the Labour Party is the facilitator of Brexit. I hate to say that, but it is true.
"In addition to all this, the possibility of the break up of the UK – narrowly avoided by the result of the Scottish referendum – is now back on the table, but this time with a context much more credible for the independence case.
"We are already seeing the destabilising impact of worry over border arrangements on the Northern Ireland peace process."
Additional reporting by Craig Fitzpatrick.