LONDON -- Former Prime Minister Tony Blair launched a new campaign Friday to persuade Britons to change their minds about leaving the European Union, arguing that those who want to remain should rise up and have their voices heard.

Blair urged voters to speak out against what he said was the government’s drive to exit the EU at any cost, arguing it could damage future generations and the unity of the country itself. In a speech for Open Britain, which is campaigning against leaving the EU’s single market of 500 million, he argued last year’s vote to leave was “based on imperfect knowledge,” and that Britons voted without knowledge of the true terms of Brexit.

“As these terms become clear, it is their right to change their mind,” he said. “Our mission is to persuade them to do so.”

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Blair’s intervention reflects the ongoing division in Britain that followed the June 23 referendum. Though the U.K. voted to leave the 28-nation bloc, the specifics under which Britain would go weren’t agreed on. Some 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,” he 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.”

Prime Minister Theresa May has offered only broad outlines on her priorities with cutting immigration being a priority. She has argued that she must keep the Europeans guessing about the U.K.’s negotiation strategy, but pressure for details has been building before she invokes Article 50, which will trigger the country’s departure from the bloc.

Blair argued that people favoring Brexit took advantage of a mood of revolt stemming in part from changes in the global economy.

“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’s not immediately clear how much support Blair may have in creating a wave of sentiment against May’s plans. The once-popular Labour leader suffered a fall from grace in supporting the United States in its intervention in Iraq that led to the ouster of Saddam Hussein.

Foreign Secretary Boris Johnson dismissed the speech and the former leader, 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 even his own party in his critique, which he declared to be ineffectual and a “facilitator of Brexit.” He also challenged elements of Britain’s media for what he described as a relentless pro-Brexit stance.

He plans to start an institute and build alliances across party lines to create a movement with 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.”