Thousands of anti-Brexit marchers descended on Westminster on Saturday to demand that Britain stays in the European Union.
Organisers estimated at least 50,000 protesters were marched through central London before converging on Parliament Square for a rally.
Sir Bob Geldof and former Liberal Democrat cabinet minister Sir Ed Davey were among those to address the crowds gathered in the square.
The People's March For Europe carries the message "unite, rethink and reject Brexit" and organisers said leaving the EU "no longer holds credibility inside Westminster, let alone on the streets of Britain".
It comes days after politicians returned to parliament following the summer recess and ahead of a critical Brexit vote.
MPs are set to vote on the repeal bill, formally known as the EU (Withdrawal) Bill, on Monday for the first time, amid concerns over the progress of Brexit negotiations.
A sea of blue and yellow Remainers amassed outside the Houses of Parliament, some draped in EU flags, while others held them aloft.
Blue wigs, berets and other headgear were in abundance, as were "Exit From Brexit" placards, while a few people could be seen wearing blue T-shirts with the words "Remoaner Till I Die".
Speaking to journalists on the sidelines of the event, Liberal Democrat leader Vince Cable said: "There's a very strong feeling I think that the whole Brexit process is a mess, it's a train crash in slow motion and we've got to find an exit from Brexit."
Crowds cheered as organiser Graham Hughes opened the event, advocating for a further referendum on Britain's membership of the EU.
He was joined on stage by a man purporting to be Foreign Secretary Boris Johnson's conscience and a Theresa May puppet.
Sir Ed Davey, Liberal Democrat MP for Kingston and Surbiton, told the crowd he was "embarrassed" for Great Britain.
He said: "I've gone from anger to distress, from fury to despair. But since the Brexit negotiations begun there's a third emotion I've been feeling.
"Embarrassment. Embarrassment at our country's leaders. Embarrassment for Great Britain."
After being interrupted by boos, he said he felt embarrassed "that these shambolic people are supposed to be representing us. They can't even negotiate".