An estimated 1 million people attended a march in London on Saturday calling for the British people to have another vote on Brexit.

"The way to break the stalemate is for parliament and the people to come together. The way to reunite our country is to decide on our future together. It’s time to say with one voice: put it to the people," Tom Watson, the Labour party's deputy leader, told the crowd in Parliament Square.

Watson on Friday tweeted he has reluctantly joined the call for a second popular vote on Brexit, saying that Brexit "is stuck in the parliamentary pipework ... the only way to resolve this is for the country to have the final say."

Protesters want a second referendum in the hope of overturning the 2016 Brexit referendum result. But Prime Minister Theresa May has consistently ruled out another nationwide vote, including in a letter sent to MPs late Friday in which she outlined four options for the U.K. government.

One of those options is for the government to revoke Article 50, which she said would be a betrayal of the Brexit referendum.

An online petition asking the British government to revoke Article 50 and stop Brexit has collected over 4 million signatures, making it the most successful petition ever posted to the parliament's website.

"I’m marching with family & friends because Brexit’s the biggest deception perpetrated on the U.K. in my lifetime. Incalculable damage to economy, international reputation, my children’s rights to live, love, work & travel freely across 27 EU countries as I did," tweeted one participant.

In October 2018 a rally asking for people to have a say on the Withdrawal Agreement drew hundreds of thousands of people — the organizers said it was 670,000. Organizers of Saturday's said an initial count put the number of demonstrators at 1 million, the Guardian reported.

The rally, organized by the People's Vote campaign and other pro-EU groups, began at 1 p.m. local time and ended in Parliament Square.

Scottish First Minister Nicola Sturgeon and London Mayor Sadiq Khan both addressed the crowd in Parliament Square.

"This is now the moment of maximum opportunity — we need to avoid both the catastrophe of no-deal and the damage which would be caused by the prime minister’s bad deal. The EU’s decision to postpone things until at least April 12 has opened a window, and those of us who oppose Brexit must seize the chance it offers," said Sturgeon.

The Scottish first minister wrote in a statement published by the Independent ahead of the rally that her party wants to ask for a longer extension to the Brexit deadline to secure enough time to organize a second referendum.

“Some say a fresh public vote will cause further division. I disagree — it is the opportunity we desperately need to heal the divisions that have only widened since the referendum," said Khan.