People have got down on one knee for an anti-racism protest in London’s Trafalgar Square despite police warning that such mass demonstrations could be viewed as unlawful.

Those who took part in the tribute to George Floyd, who died at the hands of US police, knelt two metres apart in the shadow of Nelson’s Column, wore masks and carried homemade placards which condemned racism and brutality.

A placard held by a black woman read: “I am human that is enough.”

Other banners held by the protesters, who came from different races, also said “white people must do more”, “colour is not a crime” and “no justice no peace prosecute the police”.

Deputy Assistant Commissioner Laurence Taylor earlier said that such protests should not take place under current coronavirus restrictions.

He told BBC Radio 4’s Today programme: “The health protection regulations are really clear that it is unlawful.

“The Government said that for health reasons people should not be meeting in groups of six, so we would strongly encourage people not to come out and gather in these large numbers because they are putting themselves and others at risk.

“And if they do come out, then we would ask them to observe that social distancing, think about those around them.”

His warning came after large crowds marched in London and Birmingham this week to protest about the treatment of George Floyd, 46 – a black man who died after a white officer held him down by pressing a knee into his neck in Minneapolis on May 25.

Video footage shows Mr Floyd gasping that he cannot breathe during the arrest by four officers. They have since been charged over the death which sparked days of protest in the US and Black Lives Matter (BLM) demonstrations across the world.

Clashes have broken out between police and protesters in the US, with officers recorded firing tear gas and rubber bullets on crowds. Some people looted shops.

During the Trafalgar Square demonstration, Dee Ndlovu said: “I kneel because of the names and the voices that have been lost to the wind. I kneel for the ones who are not heard and the ones who do not get a hashtag, the ones who do not get pictures or a social media campaign, the ones who have been forgotten in history and time. I kneel because of them. ”

Michael Lockwood, director general of the Independent Office for Police Conduct (IOPC), which oversees complaints made against forces in England and Wales, has urged officers to listen to ethnic minority communities.

Writing in The Independent, he said: “Right now, communities in the UK are expressing real and growing concerns about disproportionality.

“Only two weeks ago we highlighted increasing community concerns about the use of Taser.

“We are also hearing concerns about stop and search and, most recently, fines issued during lockdown being disproportionate to black people.

“There must be more research to understand issues of disproportionality, as well as assurance and scrutiny around tactics like use of force and stop and search.”

Taking a knee is a peaceful gesture to protest against police brutality which was first carried out by NFL quarterback Colin Kaepernick during the national anthem at an American Football game in 2016.

Further protests are set to take place in London at the weekend while an estimated 4,000 people are expected to attend a demonstration in Bristol, including a march through the city to Castle Park, on Sunday, Avon and Somerset police said.

Chief Constable Andy Marsh urged people to stick to social distancing measures wherever possible.

He added: “The death of George Floyd at the hands of a police officer in Minneapolis is an absolute travesty and anyone who watched that video are right to be shocked, angry, frustrated and concerned.

“It must lead to justice and accountability and we understand why people want change and to make sure their voices are heard in support of this.”

Police said protesters, many wearing protective face masks, had “made their voices clearly heard” at a demonstration in Birmingham on Thursday and there were no arrests and no disorder.

Crowds gathered in the city’s Centenary Square, where a silence was observed. Several hundred people then headed to an area outside West Midlands Police’s Lloyd House HQ, where many of them knelt or sat in the road with their fists raised.

The protest came after pockets of protesters clashed with police as thousands of people flooded into central London and abandoned social distancing for a BLM demonstration on Wednesday.

After a largely peaceful demonstration in Hyde Park, during which Star Wars actor John Boyega gave an impassioned speech, tensions later escalated outside Downing Street. There were 13 arrests.