Thousands of mostly young protesters have marched through central London in an overwhelmingly peaceful Black Lives Matter demonstration that culminated in passionate crowds gathering at the heart of Westminster. They persuaded two police officers to “take the knee” outside the gates of Downing Street in a mark of respect to American George Floyd and other black victims of police violence in the late afternoon, prompting cheers from the crowd present.

A few minutes later two demonstrators were arrested after bottles were thrown at the same group of officers, although the confrontation was short lived, and police mostly looked on as a vast crowd marched from Hyde Park to Parliament Square.

The protesters, the vast majority of whom were under 30, chanted: “No justice, no peace, no racist police” and “I cant breathe” and “the UK is not innocent” , in a lockdown-defying demonstration that was largely organised through word of mouth and social media away from established anti-racism groups.

They carried hundreds of handmade signs and called out the names of George Floyd and others in the UK like Mark Duggan who had died at the hands of police or were victims of racial injustice such as the murdered teenager Stephen Lawrence.

Frankie Clarence, 28, one of the organisers of the protest, said: “I feel we are now in a period where voices dont need to be voiceless anymore.” He was one of many who highlighted the case of Belly Mujinga, the black transport worker who died of coronavirus after being spat at at a train station.

The demonstrator added: “The British Transport Police said any assault to staff would be prosecuted, fined and arrested. After hearing the news of Belly Mujinga we found injustice and no action had been taken on her behalf. These guys are contradicting their words and theres thus injustice not just in the US, but the UK. Its literally everywhere in the world.”

Sanique Gillette, 20, from Acton, said she was there because she had a 10-year-old brother she did not want to see targeted by police when he was older simply because he was black. “It is outrageous [Floyds death]. It was in plain sight that someone was murdered.”

Others expressed disgust with Boris Johnson for not condemning the US presidents actions, shouting “fuck Boris, fuck Trump” – and accused the prime minister of racism – while others cited the everyday racism experienced in London.

Imarn Ayton, 29, said the protest was about “racism, prejudice, power and the willingness to abuse that power. Right now, currently, in 2020 in England, we have that abuse going on.”

She added: “It happened to me the other day here at a protest. I was arrested because I hurt someones feelings when I said the quote: Your ancestors would be proud. I hurt a mans feelings and he used his power and abused his power.”

Protesters brought traffic to a standstill, but there appeared to be few complaints as many car and bus drivers honked their horns in support. Some drivers accepted signs from protesters and waved them outside their window as the protest marched past.

Star Wars actor John Boyega, 28, was one of the few high-profile names present, with most public figures reluctant to be seen breaking physical distancing guidelines. The actor told fellow demonstrators he was “speaking to you from my heart”. The British actor referenced two other black Americans who died in the US, as well as Lawrences murder in London in 1993.

He said: “We are a physical representation of our support for George Floyd. We are a physical representation of our support for Sandra Bland. We are a physical representation of our support for Trayvon Martin. We are a physical representation of our support for Stephen Lawrence.”

Margaret Bernard, 60, said she had experienced racism first-hand when the National Front marched in Lewisham in 1970 and her brother had been attacked by skinheads. “My generation thought we had changed all of that,” she said.

“Words do not describe how I feel about what is happening in the US. I feel sickened, disgusted. I think this is the tip of the iceberg. Institutional racism has been happening for decades and every nation needs to address that.”

Asked what she thought of Floyds death, 17-year-old student Nayana Brathwaite said: “It is disgusting. He put a knee on his neck. As a police officer he should know that would have killed someone.”

Holding a banner bearing the name of Mark Duggan, a 29-year-old British man shot and killed by the police in 2011, Dilan, 20, said: “This is also about people who are killed in the UK. It is not just the injustice in the US, it is worldwide.

“I do not like the way Boris Johnson has reacted. He has not been telling Trump what he is doing is wrong. No one in London is condemning his actions.”

Khaya Maseko, 29, said: “Im here to stand up for my people. Its terrible that an injustice that happened to George Floyd had to happen but it has sparked this movement to really uncover what has been going on for a very, very, very long time. People have just been ignorant to it.”

Sarah Palmer, 20, a student at Durham University, was one of the many young white people showing solidarity. “I am on the side of justice. Racism may not be always in your face here where there is white brutality but I think it is definitely embedded in our culture,” she said.

Satellite demonstrations were also held around the capital, including one in Brixton, south London, where 100 people were present at an event organised by a group of friends. Protest organiser Akira said: “We have institutional racism in the UK, and we have police brutality in the UK, but we are looking at this like its an American problem and Britain has struggled with this for a long time.”