Leading speeches in Parliament Square, Delia said people were not fully informed when they voted but now understood "the dire consequences".
One placard hoisted aloft in the crowd said: '56% say protect Good Friday'. The opposition Labour party's Brexit spokesman said last month his party open to a second referendum with the option of staying in the bloc in certain circumstances. "The people voted and this government will deliver on it".
The march was followed by a rally in Parliament Square with London Mayor Sadiq Khan, as well as Nicola Sturgeon, the SNP leader, addressing the crowd.
"More than 150 coaches will bring people from towns and cities from every region and nation", they said in a statement.
Famous faces joined an estimated half a million anti-Brexit campaigners who gathered in central London calling for a second referendum.
Organisers of the so-called People's Vote March are asking people to dress up their favourite pets in costumes so that they could bark along the scenic route through the historic heart of London.
London Mayor Sadiq Khan said yesterday's event was a "march for the future" for young Britons, including those who were too young to vote in Britain's 2016 European Union membership referendum, when those who favor leaving the bloc won by 52 per cent to 48 per cent.
The thorniest issue of all is the question of Northern Ireland, which is part of the United Kingdom but shares a border with the Irish Republic that is now open to goods and people.
Khan and Liberal Democrat leader Vince Cable were among those due to speak at a rally across the street from the Houses of Parliament as the march wound its way through the capital.
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When asked if he was glad of a build-up without speculation about his own future, Mourinho said: "I hope so". In any case, United's manager was not in a mood to prolong the argument.
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This is something which has already been ruled out by Prime Minister Theresa May.
He said: 'I can't think of anything more democratic, anything more British, than trusting the judgement of the British people.
In a video message of support, 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 European Union".
What's important is now we know what the outcomes of these negotiations are.
The 69-year-old from South Devon said: "This is the first time in my life I've been political".
At the other end of the age spectrum, Joe Trickey from Croydon celebrated his 83rd birthday at the march.
He said: "I believe very strongly in the European Union as a place of peace and strength".
Dr Mike Galsworthy, from NHS Against Brexit, told BBC News: "Whether you voted leave, or whether you voted remain - when a contract comes back, you do have the right to read the small print and say actually "no, no, no, this isn't what we want to be signing up for". Pro-EU campaigners argue that the British public has been misled with false promises, and that a hard Brexit will leave everyone worse off.
He added: "I don't think you can re-run the referendum".