With organisers of the People's March estimating that 600,000 people were marching by lunchtime, making the march the second biggest protest of the century.
MPs from the Tories, Labour, Lib Dems and Green Party will join the march for a "People's Vote". Neither the United Kingdom nor Ireland want to change that situation but the European Union is insisting that once the United Kingdom leaves, some form of border controls should be established.
Protesters told of virtual gridlock on the streets of London as they called for a final say on Brexit. They are anxious about the impact on jobs, on public services like our NHS, on communities right across the country.
Tomorrow is the People's Vote rally in Central London, and it's so important that even MPs are urging people to attend.
Organizers want the public to have a final say on the government's Brexit deal with the European Union, arguing that new facts have come to light about the costs and complexity of Britain's exit from the bloc since Britons voted to leave in 2016.
Council leader Keith House added: "All evidence is that Brexit will cost jobs in all our communities, push up prices and hit hardest those people that have had the toughest time with forced austerity". They have no faith in the government to deliver the promises that were made in 2016 partly because they cannot be delivered because they never could be. That was their plan from the moment 17.4 million people delivered the "wrong" decision.
Celebrity cook Delia Smith, Dragons' Den businesswoman Deborah Meaden and London Mayor Sadiq Khan are among the speakers at the event, which is being compered by broadcasters Richard Bacon and Mariella Frostrup.
Brendan Heading, a 39-year-old IT worker, said he was anxious the decision to leave the European Union would damage the economy and could lead to the break up of the United Kingdom. That's why we need clarity and a #PeoplesVote.
She studies Spanish and is due to study overseas next year, but said "no-one knows what will happen with Erasmus funding".
Receiving cheers from the crowds, he said: "There is no deal better than the one we have now: it is better for Britain and better for Europe".
May's government - including the Prime Minister herself as well as her Chancellor and, till recently, her Home Secretary - is now controlled by a faction of Remainers.
In this week's UpFront, we debate Brexit and the prospects of both a suitable deal and a second referendum.
Emma Stevens and Emily Longman are two of the students leading the march behind a People's Vote banner.
She said: "We're both Spanish students due to study overseas next year, but no one knows what will happen with Erasmus funding".
Today thousands will gather for #PeoplesVoteMarch.
"Nobody was saying we won't have access to the single market, nobody was talking about damaging the NHS, and so we should ask the British public, wit the option of staying in the EU".
Do not let them tell you the choice is between no deal and a bad deal.
What this suggests is that, just like in the U.S., Britain has a major problem with a Deep State which is acting to preserve its own interests and against those of ordinary people.