Anti-Brexit Protesters Descend on London as Parliament Debates

LONDON — As lawmakers huddled inside the House of Commons on Saturday to debate Prime Minister Boris Johnson’s Brexit deal, huge crowds of protesters gathered outside the Palace of Westminster to demand that voters be given the final say on Brexit.

Organizers said they hoped to draw more than a million protesters, which would make it one of the largest demonstrations in British history, and by noon tens of thousands of people were already filling the streets.

Many of the protesters were demanding a second referendum on any Brexit deal that lawmakers approve.

“We are now reaching a crucial moment in the Brexit crisis,” the organizers of the demonstration, called the People’s Vote March, said in a statement. “The government has adopted the slogan ‘Get Brexit Done’ to try and browbeat an exhausted public into accepting whatever botched Brexit Boris Johnson presents to them, but we know this slogan is a lie.”

Carrying banners and waving the blue and gold-starred flag of the European Union alongside the red, white and blue of the Union Jack, they marched from the center of London, through Trafalgar Square and past the many monuments to past days of imperial power.

Even as the protesters were assembling on the streets, Mr. Johnson was making the case to Parliament that it was time for lawmakers to pass “a deal that can heal the rift in British politics” and “unite the warring instincts in our soul.”

It was the first time the House of Commons had been called into session on a Saturday in nearly four decades, when lawmakers gathered to discuss the war in the Falkland Islands.

In a referendum three years ago, British voters narrowly supported leaving the European Union, which it had joined in 1973.

Those three years have been marked by division, frustration, confusion, sadness and despair.

And growing public anger.

Out on the streets, Milou de Castellane, 52, who works as a child minder in London, said she had voted to remain in the European Union and would like the ultimate choice to be left to the people.

“There is no tangible evidence that there is any benefit to us leaving the European Union,” she said. “But there is plenty of evidence to the detriment of us leaving. We will suffer in the economy and our strength in the world community if we leave.”

She acknowledged that many had “Brexit fatigue” and that protesters might just be shouting into the wind, but she said it was still important to make her voice heard.

“I hope that the deal will not pass,” she said. “But I have a sinking feeling that it might.”

Even before Saturday, the anger over Brexit had led to some of the largest protests in British history.

The first People’s Vote March, which drew hundreds of thousands people, was held a year ago on the eve of a vote on an agreement put forth by Theresa May, who was then prime minister.

Mrs. May tried to persuade Parliament to pass her deal three times, and three times failed. Supporters of a people’s vote had hoped that the chaos would help build support for their cause.

But after her resignation, Mr. Johnson, a champion of Brexit, won the Conservative Party’s backing to take up residence at 10 Downing Street and set about pushing for a swift exit, deal or no deal.

He has steadfastly opposed the idea of another vote, saying that the people have already had their say.

Those who took to the streets on Saturday called that argument flawed.

They say that voters were misled before the referendum and that they should be given a chance to vote on a specific Brexit deal — with the benefit of being informed by years of debate and discussion — rather than the abstract notion of a withdrawal.

The protesters were joined by the former prime ministers Tony Blair, of the Labour Party, and John Major, a Conservative, who united to make a short film that was to be screened at the rally warning about the dangers Brexit posed to Northern Ireland, which is part of the United Kingdom.

Organizers opposing Brexit have sought to build support outside London and have staged rallies around Britain, including in Glasgow and Edinburgh in Scotland; in Belfast, Northern Ireland; and in Cheltenham, in southern England.

On Saturday, more than 170 buses had been arranged to bring protesters from around the country into London.

In Parliament, Jeremy Corbyn, Britain’s left-wing opposition leader, cited those gathered outside in his rebuke of Mr. Johnson’s deal.

“The people should have the final say,” he said.

Anna Schaverien contributed reporting.