Thousands of second referendum supporters were marching on Parliament asking for a vote on Boris Johnson’s Brexit deal.
Effigies of the Prime Minister, and pets draped in EU flags have been pictured at the People’s Vote march to Westminster.
Sadiq Khan was standing at the front of the rally as it set off from Park Lane on Saturday afternoon.
The Labour Mayor of London had previously called on people to join the march, writing in The Independent on Friday that he wanted to “make sure our message is heard loud and clear over the jeers and sneers in the House of Commons”.
One group of protesters were seen near Downing Street, pulling a float depicting top aide Dominic Cummings using Mr Johnson as a puppet.
With Demonic Cummings splashed across its forehead, the figure on the float appears to be wearing a Nazi uniform, including an armband which reads Get Brexit Done, and has a Union Jack moustache.
At the start of the march route, morris dancers, some wearing Morris Against Boris t-shirts, performed a routine before the protesters set off.
They are due to walk through central London to Parliament Square, where protesters will hear speeches from politicians and celebrities who support a confirmatory vote.
Among the speakers will be former deputy Conservative leader, Lord Heseltine.
However, Lord Heseltine will be speaking to campaigners on both sides of the Brexit debate, as pro-Brexit protesters have also gathered in Parliament Square ahead of Saturday’s votes.
Liberal Democrat MP and People’s Vote supporter, Chuka Umunna apologised for missing the march, and told campaigners “we are making the same argument in the House of Commons right now!”
People’s Vote organisers are also asking people to sign a letter to Mr Johnson, EU leaders, MPs, and MEPs, asking them to allow “the chance to check whether we want to proceed with Brexit”.
In an email to supporters this morning, shadow Brexit secretary Sir Keir Starmer said the letter “asks them to honour our shared democratic values, it asks them not to turn away from us now and deny us the chance for a final say.
“Add your name to the letter now and send a message to the powerful.”
Meanwhile, Brexit supporters were campaigning in Manchester.
A small group of protesters are preparing to take part in the march for democracy in the city on Saturday afternoon.