Protesters at a central London anti-lockdown rally scuffled with police officers on Saturday who were trying to break up the demonstration because of a lack of social distancing.
Police said 10 people had been arrested and four officers injured, including two who required hospital treatment.
"We continue to urge crowds to disperse," the police said on Twitter.
Chanting "Freedom" and carrying banners saying "We Do Not Consent" and "COVID 1984", thousands of people had crammed into Trafalgar Square to protest against restrictions to limit the spread of coronavirus.
Many told broadcasters they believed the pandemic was a hoax created by governments to control people.
The police ordered the protest to disperse because demonstrators had failed to socially distance or wear masks, meaning it was no longer exempt from national rules that limit gatherings to six people.
Video footage showed officers briefly using batons to drive the protesters back.
"We want to be clear, this protest is no longer exempt from the regulations," the Metropolitan Police said on Twitter.
"We are asking those attending to disperse. Sadly, some officers have been injured while engaging with people."
Saturday's demonstration followed a similar event last weekend when 32 people were arrested for offences including violent disorder and assaulting an emergency worker.
Two officers suffered minor injuries at that protest.
Prime Minister Boris Johnson tightened COVID-19 restrictions this week, telling people to work from home if possible and ordering pubs and restaurants to close early after cases started to rise again.
The United Kingdom recorded 6,042 new cases of COVID-19, official figures showed on Saturday, and 34 new deaths among those who tested positive for the virus within 28 days.
Australian Associated Press
