One supporter of the Brexit Betrayal march was carrying a huge noose and gallows because he said it represented what “traitor” Theresa May deserves.
The man, who identified himself as Laukan Creasey, from Stevenage, was widely condemned on social media for bringing the noose to the protest.
He told the Press Association he had brought it along because: “That’s what the traitor May deserves. That’s what treasonous people get.”
He later told freelance reporter Trent Murray: “Hanging was banned years ago, it’s purely a symbol.”
Another banner that was being held up by the protesters described the Prime Minister as “Theresa ‘treason’ May” and showed silhouettes of the Prime Minister with knives stuck in her back.
In October, an anonymous Tory MP was widely condemned by politicians on all sides when they were quoted as saying that Mrs May should “bring her own noose” to a meeting of the Conservative party’s 1922 backbench committee.
Sunday’s march was led by former EDL leader Mr Robinson with the crowds chanting “Oh, Tommy Tommy” and “What do we want? Brexit. When do we want it? Now.”
A counter-protest was taking place organised by Oppose Tommy Robinson in London and United Against Facism and Racism.
Scores of police officers lined the route to keep the two groups of demonstrators separated with some forced to hold people back.
By 4.30pm, a Scotland Yard spokesman said three people had been arrested.
One, the Met confirmed was arrested on suspicion of assault, another was arrested for a public order offence and the third was arrested on suspicion of possessing an offensive weapon.
Taking to the stage when the Brexit protest reached Parliament Street, Mr Robinson addressed the crowd and said: “What a beautiful sight.”
He joked: “Look at all these tattooed thugs.”
Mr Robinson added: “What you’ve witnessed this week by the establishment is fear. They fear a movement that can be politicised across this country.”
He went on: “I want to thank Ukip and Gerard Batten and Nigel Farage.
“And to anyone who fought to bring us that referendum. Now they are being slandered and attacked.”
Praising Ukip leader Mr Batten, who has faced a series of resignations this week because he hired Mr Robinson as an adviser, he said: “The amount of pressure on Gerard Batten, and he is still standing here… that is a leader.”
Mr Batten told supporters: “My message to Parliament is clear and simple: dump the deal and take Britain out of the EU now.
He added: “The only way we will ever achieve a real exit from the EU is to rebuild the Ukip electoral threat once again.”
Mr Robinson also attempted to talk people through the process of joining Ukip on their smartphones but he then joked that his bank details had been declined.
Conditions had been imposed upon the Brexit Betrayal Rally and also upon a counter march planned by Oppose Tommy Robinson in London and United against Facism and Racism.
Police had warned protesters against committing violence and causing disorder.
The rally was taking place just two days before parliament’s crucial vote on Theresa May’s Brexit deal.