PICTURES: Protesters flooded central London in defiance of the Brexit vote
The "March for Europe" rally was organised on social media and quickly turned into a massive demonstration that washed through London's political heartland of Westminster.
The two-mile route started in Park Lane, in the affluent area of Mayfair, before ending in Parliament Square.
One of the organisers of the rally, Mark Thomas, told the BBC that he was partly responsible for rallying people to protest because he felt "anger, frustration" and a "need to do something."