Thousands of people have shut their doors and windows in a wave of violent protests over the murder of Freddie Gray and the death of Freddie Robinson, two black men killed by police officers in the US last year.
In the UK, hundreds of thousands have closed their windows since the protests began, in the first wave in February and March.
The protests have also sparked violent confrontations between protesters and police.
At least 10 people were killed in the protests in the United States.
In Britain, protests have continued since the deaths of Gray and Robinson, and there are fears of further unrest.
UK Prime Minister Theresa May said on Monday that she had told her US counterpart to “keep calm and keep calm in the face of violence”.
US President Donald Trump said on Friday that the protests would not stop.
The demonstrations in Britain came amid rising tensions between the UK and US over trade.
The White House said the UK had been the first country to impose a trade embargo on the US.
“The US has failed its people and the world,” May said.
“Britain is now the second largest trading partner of the United Kingdom and we will not be cowed.”
May’s warning came as US Secretary of State Rex Tillerson urged Britain to keep calm, but also to stand up for its interests.
“We cannot be complacent, we cannot be lulled into complacency,” Tillerson said.
May’s remarks come amid growing anger among many British people about the state of relations between the two countries, which are at odds over the death in the streets of the two black Americans.