An estimated 700,000 people gathered in central London to call for a second referendum on a final Brexit deal.
Some 1,000 young activists led the so-called “march for the future” from Park Lane towards a rally in Parliament Square.
There, demonstrators from across the UK heard speeches from household names including television presenter Delia Smith and London mayor Sadiq Khan.
“We were the few, and now we are the many,” Conservative MP Anna Soubry told the crowds at the largest protest in the UK since the 2003 demonstrations over the Iraq war.
“We are winning the argument and we are winning the argument most importantly against those who voted Leave,” she added.
Christian Broughton, editor of The Independent, told marchers: “Theresa May says that the Final Say referendum will be a politicians’ vote, not a people’s vote, but we can all remember what some politicians told us in 2016.
“We, the people, can all now see what’s really coming. And from where I’m standing it looks like a people’s vote to me.”
Nearly 950,000 people have signed The Independent‘s petition urging Theresa May to call a referendum on the final Brexit deal.
Conservative MP Sarah Wollaston said calls for a People’s Vote could ”no longer be ignored” and urged Labour Jeremy Corbyn to back the campaign.
“If we had the whole of the Labour Party, as well as the SNP, the Liberal Demcorats, and obviously a very significant number of my colleagues, we would get it past it,” she said. “We need him to come behind it.”
London mayor Sadiq Khan, Green Party MP Caroline Lucas, Liberal Democrat leader Vince Cable, and Labour MP Chuka Umunna all addressed the crowd at the march.
In a video message, Nicola Sturgeon, the First Minister of Scotland, said: “Let me say this loudly and clearly, if the issue comes before the House of Commons, SNP MPs will support a People’s Vote which includes the option to remain in the EU.”
Read how we covered the march live below.
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Hello and welcome to The Independent's liveblog that follows the People's Vote march. The Final Say petition demanding a vote on any deal Theresa May secures has almost reached 1 million signatures.
Writing in The Independent, Liberal Democrat leader Sir Vince Cable, 75, and youth campaigner Femi Oluwole said it was time for all sides to accept that young people have been “forsaken” by the older generation.
In a joint piece, they said: “The march is a demonstration of young people’s anger that their futures have been unnecessarily compromised.
“But it is also a show of the growing realisation that Brexit is not inevitable, whatever the likes of Boris Johnson and Nigel Farage might want us to believe.
“Young people can still look forward to a bright future, but to achieve that we need to up the pressure for a People’s Vote – and then win it.”
Coaches filled with demonstrators are travelling from all over the UK to central London.
London mayor Sadiq Khan, who will be speaking later, has said on Twitter: "There's nothing more democratic than trusting the people to have the final say on our future."
The Independent's view on the People's Vote march: "Britain is a bitterly divided nation, but it is also a better informed one after years of discussion about the single market, customs unions and the Good Friday Agreement. It is time for an informed expression of consent. The government needs to be told that loud and clear."
Comedian Steve Coogan is among those calling for a vote on the outcome of Brexit.
Writing in The Independent, the TV star described the Brexit deal being delivered by the government as a “looming disaster for our country”, and said the public had to be given a final say on whether to accept it or not.
The actor has paid for coaches to bring people from across the UK to London, he said.
Where and when will the march take place?
Demonstrators will assemble from midday near the Hilton hotel on Park Lane in central London, before marching along the eastern edge of Hyde Park.
Protesters will then turn onto Piccadilly, before proceeding along St James Street and Pall Mall to get to Trafalgar Square.
Crowds will head down Whitehall, past Downing Street, before finally gathering in Parliament Square.
Here, the crowds will hear speeches in support of a People’s Vote from 2pm onwards.
Follow us here for live video of the march from midday.
Dominic Grieve, the former attorney for England and Wales, has told the BBC's Today programme the Britain is "reaching a dead end". Listen here:
Almost 20 MPs from the main parties have spoken in favour of giving the British public the final say through a vote on the outcome of negotiations.
Conservative MPs including Dominic Grieve, Anna Soubry, Sarah Wollaston and Heidi Allen have joined a raft of Labour backbenchers and Liberal democrats to call for a fresh public vote.
Richard Tice, founder of Leave Means Leave, has said the demonstrators need to "get over" the outcome of the 2016 referendum.
"This is a march by people who are basically losers," he told the BBC.
"They lost the vote in 2016, they then lost again in 2017. And these people, whether it's 50,000 or 100,000 people, they think they know more than the 17.4 million people who voted to take back of our laws, trade and borders (sic)."
He continued: "They cannot accept that they have lost. They need to get over it.
"The idea of a second referendum would be incredibly damaging, most of all to the trust in democracy from people up and down this country."