LONDON — Former British Prime Minister Tony Blair launched a campaign Friday to persuade the UK to rethink its decision to leave the European Union, saying those who want to remain should rise up and make their wishes known.

Former British Prime Minister Tony Blair delivers a keynote speech at a pro-Europe event in London, Britain, February 17, 2017.??[Photo/Agencies]

Blair argued that the Conservative government's drive to leave the EU "at any cost" will hurt future generations and damage the unity of the country itself.

Last year's vote to leave the 28-nation bloc was "based on imperfect knowledge" and Britons made their decision without knowing the true terms of Brexit, he said in a speech in London.

"As these terms become clear, it is their right to change their mind," said Blair, the former Labour leader. "Our mission is to persuade them to do so."Blair's intervention reflects the bitter divide that has gripped Britain since the June 23 referendum. While 51.9 percent voted to leave the EU, the terms were not specified and Conservative Prime Minister Theresa May has been reluctant to discuss her plans fearing it will hurt the UK's bargaining position.

Many in this country of 64 million have expressed disquiet at the potential consequences.

"They will say we don't represent the people. We do, many millions of them, and with determination, many millions more," Blair said. "They will claim we're dividing the country by making the case. It is they who divide our country - generation from generation, North from South, Scotland from England, those born here from those who came to our country precisely because of what they thought it stood for and what they admired."Blair spoke on behalf of Open Britain, which is campaigning for the government's Brexit legislation to be amended to ensure that Parliament has "proper scrutiny" over any deal May negotiates with EU leaders. Among the group's goals is for Britain to remain part of the bloc's single market, guaranteeing unfettered access to 500 million people.

May has offered only broad outlines of her strategy, with reducing immigration a priority. She has argued that she must keep the Europeans guessing about the U.K.'s negotiation position, but pressure for details has been building as she prepares to invoke Article 50, which will trigger Britain's departure from the bloc.

While supporters oppose any attempt to slow the drive toward Brexit, calling that undemocratic, Blair argued that the people have a right to change their minds. The leave campaign benefited from a mood of revolt stemming in part from changes in the global economy, but such opinions aren't set in stone, he said.

"The Brexiteers were the beneficiaries of this wave. Now they want to freeze it to a day in June 2016," he said. "They will say the will of the people can't alter. It can. They will say leaving is inevitable. It isn't."It wasn't immediately clear how much support Blair may have in creating a wave of sentiment against May's plans. The once-popular Labour Party leader suffered a fall from grace after he supported the United States in its intervention in Iraq.

Foreign Secretary Boris Johnson dismissed the speech, telling the BBC that people should "rise up and turn off the TV" when Blair comes on.

Blair was well aware he would be criticized and didn't spare his own party in his critique, declaring Labour to be ineffectual and a "facilitator of Brexit." He also challenged sections of Britain's media for what he described as a relentless pro-Brexit stance.

Blair said he plans to build alliances across party lines to create a movement that has the weight and reach to fight back.

"This is not the time for retreat, indifference or despair," he said. "But the time to rise up in defense for what we believe."