Two men were arrested at Tommy Robinson’s London rally on Saturday after an anti-racism campaigner was attacked, police said.
The Stand Up To Racism activist was taking part in a counter-demonstration when he “sustained a head injury” at the Victoria Embankment Gardens, according to the Metropolitan Police.
Both men were arrested on suspicion of “grievous bodily harm-level assault”, they added.
He was given first aid by officers and will be taken to hospital to be checked,” a force spokesman said.
“We are aware of some suggestions on social media that the arrests were related to the carrying of a flag, which is not the case.”
Thousands of people attended the ‘unity’ march from the Royal Courts of Justice to Trafalgar Square on Saturday.
Some 1,000 Met Police officers were deployed to monitor the event, which sparked a counter demonstration by Jeremy Corbyn’s Peace & Justice group, Stand Up To Racism, among others.
The counter-protesters marched from Russell Square to Whitehall, supported by a number of trade unions, the Stop The War coalition, Unite Against Fascism, and others.
Supporters of Mr Robinson, whose real name is Stephen Yaxley Lennon, filled up The Strand waving the flags of England, Scotland, Wales, and the UK outside the Royal Courts of Justice.
Chants were heard of “Rule Britannia”, Mr Robinson’s name, and “we want our country back”.
One man was seen with a T-shirt that read: “I identify as English”, while others had Donald Trump merchandise.
Several Israeli flags were also being flown. At one point, a man walked past the protests with a Palestinian flag and attendees could be heard booing.
They moved from the Royal Courts of Justice to a rally in Trafalgar Square at around 12.45pm.
When they arrived, a band performed and Mr Robinson addressed the crowds.
Ahead of the march, the far-right activist rallied his followers on social media early on Saturday, claiming: “Today the people of Britain will send a message to the world.
“We will remain silent no longer. WE WANT OUR COUNTRY BACK.”
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Metropolitan Police Chief Superintendent Colin Wingrove, who is in charge of this weekend’s operation, warned police will “intervene decisively” to deal with protesters who break the strict conditions about when and where they are allowed to demonstrate.
He added a “significant number” of officers are on duty as part of “a carefully planned operation” in an effort to keep people safe and prevent crime.