Thousands of people demonstrated in central London as part of a "Brexit Betrayal" march led by Tommy Robinson and UKIP leader Gerard Batten.
The founder of the English Defence League and UKIP members marched with supporter through the streets of London before a rally off Parliament Square.
The crowd loudly booed when UKIP leader Gerard Batten brought up "Remainer" May and they cheered on his reference to a "treasonous political class".
UKIP leader Gerard Batten addressing the "Brexit Betrayal" protesters near Parliament Square, London. Image: Gareth Fuller/PA Wire
Batten warned not leaving the European Union would cause the "biggest constitutional crisis'
He said: "If Parliament does not take Britain out of the European Union it will be the biggest constitutional crisis since the English Civil War.
"In 1642 the king put himself in opposition to parliament. Parliament won and the king lost his head.
"If Parliament betrays Brexit they will be putting themselves in opposition of the people and if they win you will lose your liberty."
Some of the “Brexit Betrayal” protesters wore yellow high-visibility vests in solidarity with “yellow vest” protesters in France, who are demonstrating against fuel tax and high living costs.
'They fear our movement'
Tommy Robinson addressing the crowd near Parliament Square in London. Image: Gareth Fuller/PA Wire
Robinson recieved the loudest cheers of the rally, with protesters chanting his name throughout the march.
He started his speech referencing the police restrictions on the march and warnings of violence.
“Look at all these tattooed thugs. What you have witnessed this week from the media is fear. They fear our movement," he said.
“I was not one of the main campaigners for Brexit because I was concentrating on what has been happening with the Islamisation of Britain.
“But all the problems I fight against can’t be fixed while we are still in Brussels.”
Parliament Square after flares were set off by "Brexit Betrayal" protesters. Image: Holly Pyne.
Police were on heightened alert during the protest after "serious violence" broke out at a Robinson rally in London in June, with five officers injured when bottles and barriers were hurled at them.
Scotland Yard said it also imposed the conditions based on the "current intelligence picture".
During the "Brexit Betrayal" protest, a small group of protesters set off flares near the statue of Winston Churchill in Parliament Square.
Tommy Robinson 'represents racists'
Protesters at the counter-demonstration in London. Image: Thea de Gallier
Anti-Tommy Robinson activists assembled outside the BBC at Portland Place to protest the "Brexit Betrayal" march.
A policeman on duty told TalkRADIO it was "the plan" to keep both marches apart.
Activists from Momentum, Stand Up To Racism, Football Lads and Lasses Agains Racism and various London branches of Labour marched to Trafalgar Square, with the protest happening without incident.
Owen Jones at the counter-demonstration. Image: Thea de Gallier
Political commentator Owen Jones told TalkRADIO that Robinson, real name Stephen Yaxley-Lennon, “did not represent” Leave voters, and that Leavers and Remainers should come together to oppose him.
He said: "There are people who voted Remain and Leave on our demonstration. It is important that we say that Tommy Robinson does not represent 52% of people who voted Leave.
"He only represents fascists and racists, and we will march against fascists and racists just like those before us did."
Jon Trickett, Labour MP for Hemsworth, West Yorkshire, joined Momentum activists at the end of the march and told TalkRADIO he thought “racists are showing a more blatant exposition of those ideas”.
"This is a very important event today because there is a rising feeling that there are racists are showing a more blatant exposition of those ideas, which are hateful," he said.
"We fought a world war against the racists and the fascists and it is important that we show our support for anti-racism.
"What is so inspiring is that there are so many young people who have got the message and they understand."