Thousands of young people were taking part in “Black Lives Matter” protests in London, Manchester, Bristol, Peterborough, Cardiff, Sheffield, Newcastle and other cities across the UK on a wet and windy Saturday in defiance of orders from the home secretary Priti Patel that gatherings of more than six were illegal.

Priti was backed by the Metropolitan Police Commissioner Cressida Dick, the first woman to head Scotland Yard, who said she had instructed her officers not to “take the knee”.

The latter have become almost more loyal than the king in seizing the BLM baton passed across the Atlantic.

The demonstrators on Saturday in many cases wore masks and gloves but a separation of two metres was an impossibility as they packed Parliament Square in London and defaced the statue of Winston Churchill by spraying the plinth with the word, “ACAB” — an anarchist slogan meaning, “All Cops Are B*******”.

The demonstrators carried banners which read, “Black Lives Matter”, “No justice, no peace”, and rejected the argument that their actions risked increasing the Covid infection rate above one — this already seems to be happening in parts of northwest England — with the slogan, “There is a virus greater than Covid-19 and it’s called racism.”

The home secretary will not want to be high-handed nor will the police but Priti’s personal authority is now at stake with a challenge to law and order.

She said: “Of course, I completely understand people’s desire to express their views and to have that right to protest. But the fact of the matter is we are in a health pandemic across the United Kingdom and coronavirus is a deadly virus.

“I’d say to those that want to protest: please don’t. The regulations are very clear in terms of gatherings and mass gatherings in particular. We must put public health first at this particular time.”

And on Twitter, she emphasised: “Please for the safety of all of us, do not attend large gatherings — including protests — of more than six people this weekend.

“As (health secretary) Matt Hancock said, coronavirus remains a real threat and people must protect themselves and their families from this horrific disease.”

In his Downing Street briefing on Friday, Hancock said: “Like so many I am appalled by the death of George Floyd and I understand why people are deeply upset but we are still facing a health crisis and coronavirus remains a real threat. The reason that it is vital that people stick to the rules this weekend is to protect themselves and their family from this horrific disease.”

“So please, for the safety of your loved ones, do not attend large gatherings including demonstrations of more than six people.”

Cressida Dick was clear about the law: “Coming together in a gathering is not only unlawful but also, perhaps more importantly, it is putting yourself and your family at unnecessary risk and other people around you.”

Asked for her views on images of police officers “taking the knee” to show support for protesters in the US, she said that “we encourage our officers to talk to people”, adding that a main function of the police is “to engage in a positive manner with people.”

Britain’s most senior police officer went on to state that although she understands the sentiment behind officers taking the knee, “we won’t be kneeling during protests” in the UK.

An additional 204 coronavirus deaths have been announced in the UK, taking the country’s total death toll to 40,465. But another measure – excess deaths compared with the average for this time of the year – suggests the true figure is well in excess of 50,000, the highest in the world after the United States.

The well-known British guerrilla artist voiced his support for the BLM movement: “At first I thought I should just shut up and listen to black people about this issue. But why would I do that? It’s not their problem, it’s mine.”

He added: “People of colour are being failed by the system. The white system. Like a broken pipe flooding the apartment of the people living downstairs. The faulty system is making their life a misery, but it’s not their job to fix it. They can’t – no one will let them in the apartment upstairs.”

His post was accompanied by artwork featuring a burning US flag.

In London, the US embassy, which has moved from Grosvenor Square in Mayfair to Battersea south of the Thames, was targeted by demonstrators who “took a knee” outside the mission.

Interviewed on radio, Bengali Baroness Shami Chakrabarti, who has been sacked as Labour’s shadow attorney general by party leader Sir Keir Starmer, said she would not join the protesters but “my heart is with them”.