UK police arrested two men on Saturday following an assault on a participant in an anti-fascism protest, held to counter another nearby demonstration organised by far-right agitator Tommy Robinson.
London's Metropolitan Police said the pair were arrested on suspicion of assaulting a "Stand Up To Racism" protester in Victoria Embankment Gardens in the city centre.
Officers gave the victim first aid after he sustained a head injury in the incident, and he will be taken to hospital to be checked, according to the force.
It noted that, contrary to social media reports, the arrests were not related to the carrying of any flags.
The Met, as the London force is known, said around 1,000 officers were on duty Saturday as part of the policing operation to deal with the two rallies, as well as another protest.
Thousands gathered in the heart of the British capital from late morning for the demonstration organised by Robinson, a far-right firebrand and founder of the now defunct Islamophobic English Defence League organisation.
Meanwhile the counter-protest staged by Stand Up To Racism and others also rallied in the heart of London, with the Met imposing so-called conditions on the two marches "with the aim of preventing serious disruption".
They included requiring participants to stick to certain areas and streets and disperse by stipulated times.
"Our first priority is to keep the peace to ensure that those exercising their right to lawful protest can do so safely," Chief Superintendent Colin Wingrove said ahead of the weekend events.