Demonstrators have flooded the streets of central London as they marched on Parliament to demand the public are given a final say over Brexit.

Thousands of marchers set off from Hyde Park Corner at about noon on Saturday as part of the Put It To The People protest.

Marching bands, whistles, chants and cheers provided a noisy backdrop to the march.

Demonstrators wore blue and yellow berets and flew large EU flags above the crowd as the march slowly made its way to Parliament Square.

Organisers of the protest claimed one million people joined the procession through the capital.

Protesters take part in the Put It To The People march on Whitehall in London, England. Photograph: Dan Kitwood/Getty Images

Placards on the march bore messages urging the British government to “revoke article 50” and for the issue of Brexit to be put to the people.

The size of the crowd saw people spill over into the capital’s side streets and some underground trains were not stopping at Green Park station.

The march featured people of all ages who were led in chants for a “People’s Vote”.

Many people wore yellow fluorescent stickers reading: “Bollocks to Brexit. It’s not a done deal.”

The day’s activities were kicked off by the unfurling of a large banner on Westminster Bridge that read: “Love socialism, hate Brexit.”

The stunt was organised by a group calling itself the “Left Bloc” which is supported by Labour MPs, including Clive Lewis and Kate Osamor, Green Party MP Caroline Lucas, trade unions and grassroots campaigners.

Massive crowds at #PutIttothePeople rally in London today. Good to be there. pic.twitter.com/hgY2kZaW0c — Nicola Sturgeon (@NicolaSturgeon) March 23, 2019

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Addressing a rally in Parliament Square for the demonstrators, Labour’s deputy leader Tom Watson said: “Brexit is stuck in the parliamentary pipeworks and it’s not going to find a way out.”

Addressing British prime minister Theresa May, he said: “I can only vote for a deal if you let the people vote on it too.

“Prime minister, you’ve lost control of this process, you’re plunging the country into chaos, let the people take control.”

An 800sq m banner of a David Davis quote is held up in Parliament Square during the Put It To The People march in London, Britain. Photograph: Jiri Rezac/Led By Donkeys/PA Wire

Scotland’s first minister Nicola Sturgeon told the crowd that Mrs May had pitched “parliament against the people”.

“If that is your view, prime minister, let the people speak,” she said. Ms Sturgeon accused Mrs May of being “in thrall to hardline Brexiteers”. She also called on Labour leader Jeremy Corbyn to back a People’s Vote.

Also speaking from the stage in Parliament Square, mayor of London Sadiq Khan said he was “a proud European”.

“No matter how you voted in the referendum, no matter what political party you support, we can all agree that Brexit has been a complete and utter mess,” he said. “With days to go we’re in danger of falling off the cliff, which will have catastrophic consequences.”

Mr Khan said it was “time to withdraw article 50”. He added: “It’s time to give us, the British people, a final say on Brexit.”

Other speakers included former Tory turned independent MP Anna Soubry and Labour MP David Lammy, who led the crowd in chants of “Theresa May must go” and claimed leading Brexiteers had “lied” to the country during the referendum.

Long journey

Marchers arrived in the capital from across the country, with one taking on a 1,150km journey on ferries, trains and buses from Orkney in Scotland.

Anti-Brexit campaigners take part in a march in London on Saturday. Photograph: Yui Mok/PA Wire

Saturday’s demonstrations follow EU leaders agreeing to delay Brexit to give British prime minister Theresa May a final chance to get her withdrawal deal through Parliament.

Leaders agreed to extend Brexit to May 22nd if Mrs May can get MPs to back her deal in the Commons at the third time of asking.

If the vote is not passed, the UK will have to set out an alternative way forward by April 12th, which could mean a much longer delay – with the UK required to hold elections to the European Parliament – or leaving without a deal at all.

Former Conservative chancellor George Osborne on Saturday called for a long delay to the Brexit process.

“The best outcome now would be a long delay, and it’s not the worst thing in the world to ask people to vote for some MEPs, and certainly better than stockpiling medicine and turning Kent into a car park,” he told BBC’s Today.

“So I think the best outcome is a long delay where we rethink how we deliver on the referendum result and we try and find a majority for a compromise Brexit agreement and possibly have a second referendum.”

An online petition demanding the government stops the Brexit process had topped four million signatures by Saturday morning.

It is now the most popular petition ever submitted to the Parliament website, moving ahead of a 2016 petition calling for a second referendum on EU membership.

The London march coincides with pro-Brexit campaigners continuing their long hike from the northeast of Britain to the capital.

Former Ukip leader Nigel Farage re-joined the March to Leave when it set off from Linby, near Nottingham, on Saturday morning. – PA