More than 240,000 people have signed a letter within the past 48 hours demanding a Final Say referendum on Brexit.

The letter, organised by People’s Vote and The Independent, calls on officials in the UK and European Union to do all they can to allow the British public to confirm whether any final deal put forward by Boris Johnson is indeed the “will of the people”.

The groundswell of support for the petition comes after a reported one million people marched on parliament on Saturday – during what was a crunch day for the prime minister’s plan to take the UK out of the bloc.

Boris Johnson’s plan to put the deal to the Commons was derailed after parliament backed an amendment withholding approval.

Crowds in Parliament Square erupted into cheers as the vote’s result was announced.

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The PM was then forced to request a Brexit extension from Brussels.

Before the final Brexit deadline on 31 October the letter will be delivered simultaneously to Downing Street and the Houses of Parliament, as well as the EU Parliament and the building in Brussels where the EU council meets.

MPs will be individually sent a list of signatories from their constituencies.

Several parliamentarians from across the Commons have called for another Brexit referendum.

John McDonnell, Diane Abbott and Emily Thornberry all spoke during a Final Say rally in central London on Saturday, while Antoinette Sandbach, a former Conservative MP, also reiterated her support for a fresh public vote.

“When the time comes to support a People’s Vote amendment, I can walk through that lobby with my head held high,” the MP, who is currently sitting as an independent, said.

Jo Swinson, the Liberal Democrat leader and Sadiq Khan, the mayor of London, also spoke at the event.

And Keir Starmer, Labour’s Brexit secretary, declared his support for the campaign in an email to supporters.

“It’s a letter from the people that will go, not only to the prime minister, every MP and MEP, as well as the head of all the heads of government among the 27 other European member states,” he said.

“It asks them to honour our shared democratic values; it asks them not to turn away from us now and deny us the chance for the final say. Whether you’re joining us today or not, add your name to the letter now and send a message to the powerful.”

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