Demonstrators have gathered in central London as thousands take part in the People's Vote march calling for a second EU referendum.
The march, which began at 12pm, will see people walk from Park Lane to Parliament Square before culminating in a rally in front of Parliament.
It comes as MPs continue to search of a way out of the Brexit impasse amid an agreement from the EU to give the UK a short delay.
Prime Minister Theresa May has said she will ditch her efforts to hold another vote on her Brexit deal if not enough people support it, which would mean the UK needs an alternative plan by April 12 or face a no deal scenario.
Protesters are set to be addressed by speakers outside the Palace of Westminster from 2pm to 3pm today.
Among the speakers at the rally are Labour's deputy leader, Tom Watson, Scotland's first minister, Nicola Sturgeon, London Mayor Sadiq Khan, Independent MP Anna Soubry and former attorney general Dominic Grieve.
Watson is expected to agree to back May's deal if she guarantees a referendum will be held on it.
He is expected to say: "I've come to the reluctant view that the only way to resolve this and have legitimacy in the eyes of the public is for the people themselves to sign it off."
Prior to the event, Khan released a statement saying: "Brexit is a complete and utter mess.
"We’re now days away from falling off a cliff edge with catastrophic consequences. Enough is enough. It’s time to take this out of the hands of politicians and put it back to the people."
"I’ll be marching on Saturday with people from every part of our country – from every walk of life – to demand that the British people get the final say," he added.