Police have urged hundreds of protesters to immediately leave an anti-vaccine, anti-lockdown protest in Trafalgar Square or face arrest.
The warning came after heated clashes between demonstrators and officers during a “Resist And Act For Freedom” rally on Saturday afternoon.
Dozens of officers, including some on horseback, were repelled by human blockades with loud cheering and chanting as they tried to make arrests.
Scotland Yard said the large crowds of people are “putting themselves and others at risk” just a day after Mayor of London Sadiq Khan warned it is “increasingly likely” restrictions will be needed to slow the spread of coronavirus in the capital, adding he was “extremely concerned” about the rate of transmission in London.
The number of cases per 100,000 people over seven days is reported to have increased in London from 18.8 to around 25.
A Metropolitan Police statement said there had been “pockets of hostility and outbreaks of violence towards officers” adding: “We will now be taking enforcement action to disperse those who remain in the area. Those who remain may get arrested.”
It went on: “It is important to remember that we are still in the middle of a global pandemic, and the changes have been introduced to help control the spread of the virus, keep everybody safe and save lives.
“We encourage those in attendance to leave the area immediately.”
Traffic around Trafalgar Square came to a halt during the demonstration, with one protester seen apparently spitting through the open window of a taxi whose driver had beeped the horn in frustration.
Rally organisers sold T-shirts bearing 5G conspiracy theories and advocating the legalisation of cannabis, with banners calling for Government scientific advisers to be sacked and declaring Covid-19 a “hoax”.
Addressing the crowd to huge cheers, organiser Kate Shemirani said: “We are the resistance.”
The protest was advertised with an image showing a vaccine bottle and urging people to “Come together, resist and act.”
One speaker at the rally, Professor Dolores Cahill of University College Dublin (UCD), expressed the view that the coronavirus vaccine will “make people sick”, going against mainstream scientific opinion.
The UCD has previously disassociated itself from views on Covid-19 aired by Prof Cahill, who also chairs the Eurosceptic Irish Freedom Party, the Irish Times reported.
Vaccines are the most effective way to prevent infectious disease and have virtually eradicated smallpox, polio and tetanus in the UK, the NHS says.
But if people stop getting vaccinated then diseases can quickly spread again, it said, pointing to a spike in measles and mumps between 2016 and 2018.
There is no evidence that vaccines cause autism, allergies or other conditions, weaken the immune system in any way, or contain harmful ingredients, it adds.
The World Health Organisation says immunisation prevents two to three million deaths per year.
Protests are exempt from new legal restrictions introduced on Monday limiting groups to six, but only if it is “organised in compliance with Covid-19 Secure guidance”, the Government said.