Hundreds of thousands of people are expected to march on the streets of London later demanding a people's vote on Brexit.
It is expected to be the biggest protest to date, as pressure builds on the prime minister over her negotiating strategy.
Many believe the UK is heading for a "no deal" or a bad deal Brexit and want to have their say.
Among the celebrities involved are actor Steve Coogan, chef Delia Smith and Dragons' Den star Deborah Meaden.
Some have even contributed to buses bringing people to the capital from all over the country.
It is thought that thousands of students will take part, many of whom were too young to have their say in the 2016 referendum.
Hilary Gyebi-Ababio, a third year student at Bristol University, told Sky News: "I was three days shy of voting against Brexit, but I feel now that if we do get a people's vote, I would be getting my voice back because I really feel like I lost it during the campaign, which is ridiculous."
Some students are coming from as far afield as Orkney, an archipelago off the northeastern coast of Scotland. They had to leave at 6am on Friday to make it in time for Saturday's rally.
Brexit has, undoubtedly, been the great divider. It has split parliament, the Conservative party, the cabinet and the nation.
The prime minister's negotiating strategy has been criticised by both sides, but she has adamantly ruled out the possibility of a people's vote, something many of her Tory colleagues are pushing for.
The former foreign secretary, Boris Johnson and Brexit secretary, David Davis have already resigned over Theresa May's so-called Chequers plan, which outlines the relationship the UK would like to have with the European Union after Brexit.
This week, she has come under even more pressure by conceding that we may have to remain tied to EU rules for longer, with an extended transition period.
0:22Co-chair of the Leave Means Leave campaign, Richard Tice said: "It is not a people's vote, it is actually a losers' vote.
"They can't accept the democratic will of the public.
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"They only accept democracy when it votes their way.
"It is a losers' vote by those who don't understand why 17.4 million people up and down the country voted to leave."
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