An estimated 7,00,000 people opposed to the the United Kingdom’s impending exit from the European March protested in London on Saturday, seeking a referendum on the final Brexit deal, the BBC reported.

The numbers were provided by the march organisers, with the Metropolitan Police refusing to confirm the figures. The march was the biggest show of public opposition to government policy since the anti-Iraq war protest in 2003, reported The Guardian.

London Mayor Sadiq Khan started the People’s Vote march to the Parliament Square in central London and addressed the crowd that also consisted of representatives from the main political parties and celebrities. Last month, Khan called for another referendum on the United Kingdom’s European Union membership and criticised the government’s handling of Brexit negotiations with the EU. Prime Minister Theresa May has already ruled out a second referendum.

“What’s really important is that those that say that a public vote is undemocratic, is unpatriotic, realise that in fact, the exact opposite is the truth,” said Khan on Saturday. “What could be more democratic, what could be more British, than trusting the judgement of the British people.”

“It’s time for this vital issue is be taken out of the hands of the politicians and returned to the British people,” said Khan, adding that the march for the voters who were too young to vote in the Brexit referendum two years ago. In June 2016, the British public voted to leave the European Union by a margin of 51.89% to 48.11%. The UK is due to leave the European Union on March 29, 2019, but the two sides are yet to agree how trade will work between them afterwards.

Foreign Office Minister Sir Alan Duncan, de facto deputy to Foreign Secretary Jeremy Hunt, said Conservative MPs and ministers now have a duty to prove they can deliver a sensible Brexit that was in the national interest.

“There simply is no ideal outcome that will suit everyone,” he said. “People have to step back from their ideological obsessions and accept a pragmatic compromise. Otherwise we risk inflicting on ourselves massive economic damage, as well as political damage, domestically and internationally, for years to come.”

The People’s Vote march was held at the same time as a pro-Brexit rally in central UK’s Harrogate, organised by the group Leave Means Leave and led by former UK Independence Party leader Nigel Farage.

May has repeatedly ruled out holding a second referendum, saying members of parliament will get to vote on whether to accept any final deal. “To ask the question all over again would be a gross betrayal of our democracy - and a betrayal of that trust,” she wrote in The Telegraph last month.