"It's OUR future. We want to stay together in Europe! At the March for Britain in Europe!," Tim Farron, the leader of the Liberal Democrats, wrote on his Twitter page.
According to organizers, the event started at 11:00 a.m. local time (10:00GMT) at the Park Lane street and the protesters then moved to the Parliament Square.
A city police spokesperson told RIA Novosti that no public order violations had been registered as of now.
On June 23, the United Kingdom held a referendum to determine whether or not the country should leave the European Union. According to the final results, 51.9 percent of voters, or 17.4 million people, decided to support Brexit, while about 16.1 million opposed it.