Disturbing footage shows a group of officers being surrounded by a masked mob forcing them to flee as glass bottles and other projectiles are launched at them.
One demonstrator was seen climbing on the national war memorial, The Cenotaph, which is dedicated to those who died in WWI, and setting fire to the Union flag.
Sunday's peaceful protests, which were spoiled by a minority of thugs, took place outside the US Embassy in a response to the death of George Floyd in Minneapolis last month.
Activists in face masks are holding placards reading "I can't breathe" to echo the final words of Floyd after held him down by kneeling on his neck.
Others have taken a kneel in solidarity with those of who have accused police of brutality on a global scale.
The densely-packed crowd also broke out into chants of "enough is enough".
Images from last night show cops and protesters clashing near Whitehall.
Other images show a police officer with blood coming down his face as colleagues treat him on the pavement.
The Home Secretary branded the escalation of violence as "lawless and reckless" last night, The Daily Mail reported.
Priti Patel described the scenes as "disgraceful vandalism" by a "thuggish minority".
And Boris Johnson tweeted: "People have a right to protest peacefully & while observing social distancing but they have no right to attack the police.
"These demonstrations have been subverted by thuggery - and they are a betrayal of the cause they purport to serve. Those responsible will be held to account."
55
Tension between cops and protesters escalate during demonstrations on King Charles StreetCredit: Getty Images - Getty
55
One man is seen tossing an object during Sunday's protestCredit: Reuters
55
Demonstrators leave their placards outside the Houses of ParliamentCredit: EPA
55
Protests in London on Sunday have largely been peacefulCredit: PA:Press Association
55
Protesters march on the US Embassy in LondonCredit: AFP or licensors
55
Black Lives Matter protesters outside the US Embassy in London on SundayCredit: London News Pictures
Met Police said 12 people were arrested on Sunday night and eight officers were injured.
Superintendent Jo Edwards, spokesperson for the protests, said: “Regrettably officers were faced with further scenes of violence and disorder following a day of predominantly peaceful protest throughout the capital.
“This is a hugely impassioned movement and we understand the public’s desire to have their voices heard – however it is not right that this passion has turned into violent attacks on officers.
“I would like to thank our officers, and those from the City of London Police and British Transport Police for their professionalism in the face of entirely unacceptable behaviour.
“Overnight our policing operation will continue and I would urge demonstrators thinking of returning to stay at home. The threat of Coronavirus remains very real, and we need you to protect yourselves, your friends and your family.”
Protests in London and the rest of the UK have mostly been peaceful throughout the weekend.
Hundreds of Black Lives Matter protesters rally outside US Embassy in London a day after 14 cops injured in clashes
55
The demonstrators have descended on London on SundayCredit: PA:Press Association
55
The protesters hold up signs in London on SundayCredit: Reuters
55
The demonstrators lie on the ground outside the embassyCredit: Reuters
55
Thousands are expected to attend the rally on SundayCredit: PA:Press Association
55
Protesters take a knee in solidarity with those who have accused the police of brutality and racismCredit: Reuters
55
The protesters are making their way to WhitehallCredit: AFP or licensors
55
A couple embrace at the march against racism and police brutality on SundayCredit: Reuters
55
A protester wears a face mask outside the US embassyCredit: AP:Associated Press
55
A statue of Edward Colston was toppled in Bristol on SundayCredit: Twitter
55
The statue was toppled by protesters in BristolCredit: PA:Press Association
Many protesters are wearing face masks to protect them against deadly coronavirus, while others are attempting to socially distance.
On Saturday, thousands met at Black Lives Matter rallies in London, Manchester, Newcastle, Cardiff and Watford.
And 14 police officers were injured - including a female cop thrown from her horse - as the protest turned violent.
Video showed her colliding with a traffic light before the horse bolted through a crowd of protesters.
The officer was taken to hospital with "nasty injuries" following the horror in Whitehall on Saturday.
55
Lewis Capaldi at a protest in Edinburgh on SundayCredit: PA:Press Association
55
Protesters in Weymouth, Dorset, on SundayCredit: Alamy Live News
55
Demonstrators march along the seafront in DorsetCredit: Alamy Live News
55
A rally is also taking place in Bristol on SundayCredit: PA:Press Association
55
BLM protesters at a rally in Edinburgh on SundayCredit: Alamy Live News
55
Protesters in Manchester on SundayCredit: London News Pictures
Earlier in the day, the Winston Churchill statue was vandalised during yesterday's Black Lives Matter protest in London's Parliament Square.
Pictures show police officers standing in front of the memorial with neon green graffiti defacing it on the 76th anniversary of D-Day.
It appears the world-famous memorial was defaced with letters ACAB - which is believed to stand for 'All Cops Are B******s'.
Other monuments were also damaged - including statues in Parliament Square daubed with the words "racist" and "f**k Boris".
55
A statue in Parliament Square is covered in graffitiCredit: Rex Features
55
The word racist was scribbled on the base of Mahatma Gandhi's statueCredit: Rex Features
55
Police stand in front of the Winston Churchill statue after it was vandalised yesterday
Metropolitan Police Commissioner Dame Cressida Dick there was "no place for violence" in the capital.
She added: "I am deeply saddened and depressed that a minority of protesters became violent towards officers in central London yesterday evening
"The number of assaults is shocking and completely unacceptable.
"I know many who were seeking to make their voices heard will be as appalled as I am by those scenes. "Officers displayed extreme patience and professionalism throughout a long and difficult day, and I thank them for that."
Health Secretary Matt Hancock has also warned there is "undoubtedly a risk" there will be an increase in coronavirus cases following the protests.
A Minneapolis officer kneels on the neck of George Floyd
55
George Floyd died after he was arrested by Minneapolis police
He said he supported the protesters' arguments, but urged: "Please don't gather in groups of more than six people because there is also a pandemic that we must address and control.
"And so we've got to make the argument, we've got to make further progress, on top of the significant progress that has been made in recent years, but we've got to do it in a way that's safe and controls the virus."
The death of dad Floyd, 46, has been classified as a homicide after an autopsy found his heart stopped as police restrained him and compressed his neck.
A separate autopsy commissioned for Floyd’s family also found he died of asphyxiation due to neck and back compression.
55
