Politicians from all parties have urged the Prime Minister to give the public the final say over Brexit at the Put it to the People march in London.
Organisers claimed around one million took part in Saturday’s event, which finished with a rally in Parliament Square.
MPs urged their parliamentary colleagues and the Government to back a new referendum on leaving the EU.
Labour’s deputy leader Tom Watson told the crowd: “At every turn we have been ignored.
“At every stage Theresa May has doubled down rather than reaching out.
“She has made it impossible for anyone who cares about jobs, about solidarity at home and abroad, about friendship across borders and between communities to support this Brexit.”
Addressing Mrs May, he called on her to “look out your window” to see “this magnificent crowd today”.
He added: “Prime Minister, you’ve lost control of this process, you’re plunging the country into chaos, let the people take control.”
Mayor of London Sadiq Khan took to the stage to call for Article 50 to be withdrawn.
“The British people didn’t vote for the Government to gamble on our future, the British people didn’t vote for the national nightmare that’s been created,” he said.
“It’s time the Government gave us, the British people, a final say on Brexit.”
A group of eight cross-party MPs also appeared in front of the crowd together to support a People’s vote.
Anna Soubry of The Independent Group, Conservatives Justine Greening and Philip Lee, Green Caroline Lucas, the Lib Dem’s Jo Swinson, the SNP’s Ian Blackford and Labour’s David Lammy and Rosena Alin Khan took it in turns to criticise the Brexit process.
Ms Soubry urged her parliamentary colleagues to “put your country first, get into the lobbies and vote for a People’s vote”.
Mr Blackford said: “No parliamentarians should be going through the lobbies to make their constituents poorer.”
Ms Greening said: “This started with a referendum, let’s finish it with a final say.”
Ms Lucas said while the PM had tried to “beg and bribe” MPs to back her deal, she was not allowing “the British people to say whether they have changed their minds in three years”.
Scotland’s First Minister Nicola Sturgeon told the crowd Mrs May had pitched “Parliament against the people”.
“If that is your view, Prime Minister, let the people speak,” she said.
Ms Sturgeon accused Ms May of being “in thrall to hardline Brexiteers”.
She also called on Labour leader Jeremy Corbyn to back a “people’s vote”.