Metropolitan Police said 12 people were arrested and eight officers injured during Sunday’s anti-racism demonstrations in central London.
Most of the arrests were related to public order offences while one was for criminal damage following an incident at the Cenotaph.
It comes after Scotland Yard said 29 people were arrested and 14 officers were injured during clashes between police and protesters the day before.
Sunday’s Black Lives Matter rallies attracted thousands of people right across the UK.
Pop superstar Lewis Capaldi was pictured alongside protesters at Holyrood Park in Edinburgh, while rapper Stormzy attended the London protest.
London Black Lives Matter also organised an online protest via Zoom for those unable to attend the demonstrations, which attracted more than 10,000 people.
Elsewhere, the operational patrol unit of Warwickshire Police tweeted the M6 southbound was temporarily closed soon after 6pm due to pedestrian protesters blocking the carriageway at Junction 3.
In Manchester, hundreds crowded into St Peter’s Square, kneeling in silence as a mark of respect for African-American man George Floyd, who died after a white police officer held him down by pressing a knee into his neck on May 25.
In Bristol, protesters toppled the bronze memorial to slave trader Edward Colston and dumped it into the harbour.
Avon and Somerset Police said they had launched an investigation and were seeking to identify those involved with the removal of the statue.
Home Secretary Priti Patel called toppling the memorial “utterly disgraceful”.
“I think that is utterly disgraceful and that speaks to the acts of public disorder that actually have now become a distraction from the cause in which people are actually protesting about and trying to empathise and sympathise,” she said.
In a statement to the BBC, the Mayor of Bristol Marvin Rees said it was “important to listen to those who found the statue to represent an affront to humanity”.
Earlier in London, free masks, gloves and hand gel were given out to the thousands of people at the US embassy for the peaceful protests.
Demonstrators flooded the streets around the embassy before marching on Westminster, protesting against racial injustice and police brutality.
South London painter and decorator Christopher Green, dressed as comic book hero Black Panther, told the PA news agency he joined the protest to “support all the people in America and all those who are being oppressed”.
The 53-year-old added: “The most important thing that people have got to do is take out their video phone and document any counter-action with police because without this simple thing with George Floyd, we would probably never have known what happened.”
Graffiti was scrawled on the statue of Sir Winston Churchill in Parliament Square, with spray paint used so the name plate read Churchill “is a racist”.
Demonstrations were carried out peacefully for much of the afternoon, but bottles were thrown at officers in one incident near the Cenotaph soon before 9pm.
The crowd – much smaller than earlier on Sunday – shouted “no justice, no peace” as they moved down Whitehall and let off smoke bombs as a police helicopter buzzed overhead.
Metropolitan Police superintendent Jo Edwards said it was regrettable that “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.”
Prime Minister Boris Johnson also said the demonstrations had been “subverted by thuggery” following the clashes between pockets of protesters and police.
On Sunday evening, Mr 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.”
Speaking to The Guardian, Labour’s shadow justice secretary David Lammy said the Government should acknowledge “racism and prejudice exist in the United Kingdom as well as the United States”.
“We must turn this moment into one of change and justice in the UK too,” he said.
British Health Secretary Matt Hancock said it is “undoubtedly a risk” that there will be an increase in Covid-19 cases following the protests, as he urged people not to gather in groups of more than six people.
Mr Hancock said he supported the activists’ arguments, but said: “Please don’t gather in groups of more than six people because there is also a pandemic that we must address and control.”