An estimated 700,000 people have gathered in central London to call for a second referendum on a final Brexit deal.
MPs from across the political spectrum and a slew of famous names took part in the People's Vote march, sponsored by The Independent as part of its Final Say campaign.
Some 1,000 young activists led the so-called "march for the future" from Park Lane towards a rally in Parliament Square.
There, demonstrators heard speeches from household names including television presenter Delia Smith and London mayor Sadiq Khan.
The Independent has urged Britain's MPs to "keep the nation's options open" as the Brexit negotiations enter their final phase.
An editorial following today's march argues the case for a second referendum will be "irresistible" if Theresa May's government is unable to reach a deal with EU negotiators.
Editorial: Beyond the march, The Independent presses MPs to keep our options open on the most important decision in generations
Whatever happens in the Brexit negotiations, politicians know that the people want their voice to be heard
More than 946,000 people have now signed The Independent's petition calling for a the public to be given a Final Say on the Brexit deal.
Thousands of signatures have flooded in today amid a huge turnout for the People's Vote march.
Addressing the rally this afternoon, The Independent's editor Christian Broughton said he had "hoped we might get as many as 20,000 signatures" when the petition launched earlier this year.
A sizeable anti-Brexit rally was also held this afternoon in Belfast, where campaigners said Europe was a force for peace in Northern Ireland.
More than a thousand people, many waving EU flags and carrying anti-DUP placards, gathered outside Belfast's city hall.
The Rally for Remain was organised to coincide with the People's Vote march in London.
Northern Ireland voted by a majority of 56 per cent to remain in the EU in the 2016 referendum.
"The EU forced nations to compromise, forced people to come together on the big issues like climate change.
"It underpinned the peace. The EU spent money underpinning the peace right across Europe, from the fall of the Berlin Wall, which could have been chaotic, right through to the former Yugoslavia.
"Nowhere did it do that more so than right here."
Conservative MP Sarah Wollaston said calls for a People's Vote "can no longer be ignored" following today's protest, urging Jeremy Corbyn to back a second referendum.
The Totnes MP, who took part in the march, said a second referendum could result in another Leave vote but "we need to be given the chance to see it".
She added: "Let people weigh up and the pros and cons of the actual deal or no deal that we're heading for and then they can give their informed consent, and for me that's the key principle here."
Ms Wollaston said the backing of Labour leader Jeremy Corbyn would "absolutely" make a difference to calls for a second referendum, adding: "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.
"We need him to come behind it."
Nigel Farage, who has been at a Leave Means Leave rally in Harrogate today, said he would be "happy to have another referendum in 20 years or so".
Speaking to Sky News, the former Ukip leader suggested holding a new vote in the near future would cause "a wave of public anger" and plunge the country "into more uncertainty".
He claimed the UK would vote to leave the EU "by a much bigger margin" in a second referendum.
Vince Cable, leader of the Liberal Democrats, said he thinks "people have woken up to the potential disaster" of Brexit.
He added: "Even if they negotiate a deal, it's going to be a bad deal, where we're going to spend years under European Union rules but have no say in them and beyond that there's a cliff edge.
"We've realised there isn't a good deal coming out of this and a lot of people are frightened, people are worried."
Addressing the rally earlier, he said it was the "majority" of his generation that voted to leave, "taking the freedom" away from young voters.
To cheers from the crowds, he added: "There is no deal better than the one we have now: it is better for Britain and better for Europe."
Conservative MP Anna Soubry told the thousands gathered in Parliament Square that "it is clear we are the many".
Addressing the cheering crowd, she added: "We are winning the argument, most importantly against those who voted leave.
"We will take responsibly and sort out this mess."
Right from the start of this debate they tried to set different parts of our United Kingdom against each other; they wanted to divide this country. And the truth is, whether you are from a Remain or Leave area, the problems are the same.
Whether you are from Liverpool, Lincoln, Llanduno, Livingston in Scotland or Lambeth, where I am, Brexit is not going to make those problems better, it is going to make them worse.
The deal on the table is nowhere near as good as the deal we've got now.
Green Party MP Caroline Lucas described the huge crowd was a "beautiful sight".
She told those gathered:
What a movement we have become.
The Green Party is proud to be part of this amazing movement for a People's Vote, because we know that democracy didn't end on the 23rd June 2016.
That referendum wasn't the end of the story; it was the start of something new.
She said Brexit "would make our poorest communities even poorer and more powerless".
"We must have that People's Vote, but we must also re-programme an economy that fails so many, that is based on such inequality, that condemns us to climate breakdown."
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.
When we started the Final Say campaign in July, our politics team hoped we might get as many as 20,000 signatures on our change.org petition.Well, this morning I checked: we had 940,000 signatures. And I'm pretty sure that by the end of today there'll be a few more.We have to keep on showing up and signing up.Only The Independent could start this campaign because it's not tied to any political party. We trust our readers, we trust our reporters and we tell it honestly as it is.
Mr Broughton then introduced politicians from across the political spectrum, including Caroline Lucas, Chuka Umunna, and Vince Cable.
The Lord Of The Rings actor said he is supporting the protest as he believes there should be a second referendum “now that people are more informed”.
Brexit must not be allowed to undermine workers' rights, says Jeremy Corbyn
As crowds rallied in London to demand a vote on the EU referendum, Jeremy Corbyn told United Nations chiefs in Geneva Brexit must not be allowed to undermine workers' rights.
The Labour leader said he would work with other countries to "resist" attempts to reduce protections for UK staff.
Mr Corbyn was in the Swiss city to meet Michelle Bachelet, UN high commissioner for human rights, and Guy Ryder, director-general of the International Labour Organisation.
He said: "Britain is leaving the EU, but we must and will work together with those in other countries to resist the pressure to undermine rights and protections at work.
"Tax dodging, speculation and unaccountable corporate power have created economic inequality on a vast scale and sucked wealth and jobs out of community after community.
"Average pay in Britain is now lower than a decade ago and workers have faced a concerted attack on their rights under this Tory Government.
"We are determined to secure stronger rights at work and fair rules for business as we leave the EU as part of a new economic settlement which delivers for the many, not the few."
PA
Please allow a moment for the live blog to load
The Independent has launched its #FinalSay campaign to demand that voters are given a voice on the final Brexit deal.
Sign our petition here
