Thousands are marching through the streets of London today as part of a Ukip-organised 'Brexit betrayal' demonstration.
Among the campaigners is English Defence League (EDL) founder Tommy Robinson who was appointed as an advisor to the party last month.
The anti-Islam activist's appointment led to a string of resignations within Ukip, including former party leader Nigel Farage.
Tommy Robinson (centre, holding a mobile phone) arrives to take part in a 'Brexit Betrayal' march and rally organised by Ukip in central London
The Brexit champion led a walk-out of major figures from the party in protest at its 'new BNP' stance, after dramatically warning the party's embattled leader Gerard Batten that Ukip must ditch its relationship with Robinson.
Mr Farage took with him a slew of senior Ukip figures, including ex-boss Paul Nuttall and Scottish leader David Coburn, both fellow Members of the European Parliament with Farage.
Today's demonstration has been opposed by counter-protesters and anti-fascist groups who're also marching the streets to oppose the 'far-right extremists'.
Tommy Robinson addresses the rally after taking part in a 'Brexit Betrayal' march organised by Ukip in central London
Oppositions organisers said the Brexiteer march was 'vastly' outnumbered by counter-demonstrators.
A Ukip spokesman said 'quite a few thousand' had turned up to its rally. Police did not provide estimates on crowd sizes.
Momentum national co-ordinator Laura Parker said: 'Today is a huge blow for Tommy Robinson and his vile, hate-fuelled politics.
Tommy Robinson (front centre) gets caught in the large crowds gathered at the 'Brexit Betrayal' march organised by UKIP
'Even with the Ukip machine in tow he only managed to bring a few thousand supporters out on the streets while we mobilised nearly 15,000 to march against his racism and bigotry.'
The protesters chanted the whole way on their specified route, shouting 'Nazi scum, off our streets'.
Among Ukip supporters was a man who gave his name as Laukan Creasey, from Stevenage, who was carrying a gallows with a noose hanging down.
Asked why he was brandishing it, Mr Creasey said: 'That's what the traitor May deserves. That's what treasonous people get.
Among Ukip supporters was a man who gave his name as Laukan Creasey, from Stevenage, who was carrying a gallows with a noose hanging down
Police officers push back counter-protesters in Trafalgar Square who came to disrupt the Brexit Betrayal march today
'It was a referendum not a never-endum. And they promised to implement whatever we decided and they haven't, so two-and-a-half years down the line this is what you get.'
The Ukip group marched to outside the Houses of Parliament where they were to be greeted by festive music and speakers.
The crowd loudly booed when Ukip leader Gerard Batten brought up 'Remainer' Mrs May and they cheered on his reference to a 'treasonous political class'.
A man demonstrating alongside the pro-Brexit UKIP section of the supporters dons a hat popularised by US President Trump
Theresa May was widely satirised as 'Treason May' among certain sections of people during the demonstrations
He added: '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.'
Their opposition march, who had started outside the BBC building in Portland Place, were separated from the Brexiters by police barriers in Whitehall.
Police officers with batons at the ready force back protesters in Trafalgar Square this afternoon
Weyman Bennett, joint convener of Stand Up To Racism and one of the march organisers, said: 'I believe that the majority of people in this country reject fascism and racism.
'There's deep concern in Britain about the growth of the far right in this country, under the guise of Tommy Robinson and Ukip.'
It comes just three days before parliament is due to make the crucial vote on Theresa May's Brexit deal with the European Union.
Police officers tackle a demonstrator to the ground as clashes break out in Trafalgar Square during protests and counter-protests
Anti-fascist campaigners wave signs that say 'refugees welcome' and 'oppose Tommy Robinson' in the streets of the capital
'Make racists afraid again' is visible within a sea of anti Tommy Robinson placards among the Labour backed demonstrators
Mr Robinson's supporters gathered to call for Brexit, with one brandishing a noose he said was for Prime Minister Theresa May.
The counter protestors outnumbered the Tommy Robinson supporters, who are thought to have mobilised around 3,000 people.
The counter demonstration was organised by Momentum and a coalition of 23 organisations including London Young Labour, Feminist anti-fascists, Labour Against Racism and Fascism and the Stop Trump Coalition.
Shadow chancellor John McDonnell urged 'all Labour members and anyone who cares about the future of our country' to attend the demonstration and praised Momentum for 'leading the way' in opposing a 'newly energised, well funded network of hate'.
'This march isn't about Brexit, it's about far-right extremists dressing up in suits and pretending to be respectable,' Mr McDonnell said.
'A newly energised, well-funded network of hate is emerging, from (former Donald Trump strategist) Steve Bannon in the US to the former EDL leader Tommy Robinson at home, and it threatens the very fabric of our nation.'
Demonstrators unhappy with Prime Minister Theresa May's Brexit negotiations show their disdain at the rally today
Among those marching against the activists (centre) were grass roots group Momentum and Unite Against Fascism
Founder and former leader of the anti-Islam English Defence League, Stephen Yaxley-Lennon, AKA Tommy Robinson attends a pro-Brexit demonstration with a gash on his head, supported by swathes of pro-Brexit campaigners
'This march isn't about Brexit, it's about far-right extremists dressing up in suits and pretending to be respectable,' Shadow chancellor John McDonnell said. A sign reading 'Brexit means exit' echoes the opinions of Robinson-backed demonstrators
People holding placards opposing Tommy Robinson take part in a separate protest ahead of a UKIP-backed Brexit betrayal rally. Their signs carry messages such as 'No to Islamophobia', something they think UKIP and Robinson facilitate
Among those marching against the activist were grass roots group Momentum and Unite Against Fascism. Anit fascism and anti Brexit marches included songs and dancing, arriving at their final stop on Whitehall to the sound of Michael Jackson's hit Black Or White.
Police have heightened concerns 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'.
Gathering outside the Dorchester Hotel, Mr Robinson's supporters marched along a specified route from Park Lane to Parliament Street.
There, police barriers separated them from counter-demonstrators who marched from outside the BBC building in Portland Place to Whitehall.
Nick Lowles, chief executive of anti-racism campaigners Hope Not Hate, was among those critical of Mr Robinson's rally.
'This is a cynical attempt by some of the most extreme voices in Britain, united in hatred for Muslims and other minorities, to exploit Brexit tensions and sow discord and hatred, much as Gerard Batten has done with Ukip and its Islamophobic charge to the right since he took over,' he said.
The counter protest takes place three days before parliament is due to make the crucial vote on Theresa May's Brexit deal with the European Union
Stephen Yaxley-Lennon, AKA Tommy Robinson (3rd L) smiles as he attends a pro-Brexit demonstration promoted by UKIP (United Kingdom Independence Party) in central London
Metropolitan Police officers marshal demonstrators during the Anti-Tommy Robinson and UKIP rally today
People holding placards opposing Tommy Robinson take part in a separate, anti-fascist action, protest
'Oppose Tommy Robinson - don't let the racists divide us' adorn the placards waved by anti Tommy Robinson demonstrators
The Metropolitan Police had appealed for both sides to protest peacefully, after some Robinson supporters praised rioting
Some of the pro-Brexit contingent took aim at the BBC for 'Fake news' - a term popularised by right wing US President Trump
Demonstrators hold flags and placards while linking arms during an Anti-Tommy Robinson rally in central London
One sign among the pro-Brexit marchers reads: 'Treason May has signed over entire British defence system'
Anti racism groups accused Tommy Robinson and UKIP of fascism and branded them 'Nazis' with some of their signage
A woman holds up a sign throwing her weight behind the pro leave camp. 'Make Brexit happen, join UKIP' the sign reads
Police officers marshal Tommy Robinson supporters away from demonstrators during the Anti-Tommy Robinson and UKIP rally
A police officer controls his police horse as demonstrators march nearby during the Anti-Tommy Robinson and UKIP rally