British Prime Minister Keir Starmer said violent protesters who had targeted Muslim communities would swiftly face the "full force of the law" as he sought to quell days of anti-immigration rioting.
The stabbing to death of three young girls in the northwest English town of Southport last week has been seized on by anti-immigrant and anti-Muslim groups, with disinformation spread online and amplified by high-profile far-right figures to spark disorder in towns and cities.
"Whatever the apparent motivation, this is not protest, it is pure violence and we will not tolerate attacks on mosques or our Muslim communities," Starmer said on Monday after an emergency meeting with police and prison chiefs.
"The full force of law will be visited on all those who are identified as having taken part."
The violence erupted last Tuesday after social media posts said the suspected attacker in Southport was a radical Islamist who had just arrived in Britain and was known to intelligence services.
Police say the 17-year-old suspect was born in Britain and they are not treating it as a terrorist incident.
Protests, mostly involving a few hundred people, have continued in towns and cities across the country, with bricks thrown at police officers, shops looted and mosques and Asian-owned businesses attacked. Cars have been set on fire and some unverified videos on social media have shown ethnic minorities being beaten up.
Interior minister Yvette Cooper said rioters had felt "emboldened by this moment to stir up racial hatred".
She promised a reckoning to those involved, saying the government would back punishments ranging from jail sentences to travel bans. Police have arrested around 420 so far.
In Rotherham, northern England, protesters tried to break into a hotel that housed asylum seekers in what Starmer called an act of "far-right thuggery".
Protests also turned violent in Liverpool, Bristol, Tamworth, Middlesbrough, Sunderland, and Belfast, in Northern Ireland, with largely young men wearing balaclavas and draped in the British flag hurling rocks and shouting "Stop the Boats", a reference to migrants arriving in dinghies on the south coast.
In some places they were met by large groups of counter protesters, with police often struggling to keep the two sides apart.
Starmer said a "standing army" of specialist police officers would tackle outbreaks of violence where needed.
Police have blamed online disinformation, amplified by high-profile figures for driving the violence.
Stephen Yaxley-Lennon, known by the pseudonym Tommy Robinson and previously the leader of the defunct anti-Islam English Defence League, has been blamed by media for spreading misinformation to his 875,000 followers on X.
"They are lying to you all," Yaxley-Lennon said. "Attempting to turn the nation against me. I need you, you are my voice."
Elon Musk, the owner of X, also weighed in. Responding to a post on X that blamed mass migration and open borders for the disorder in Britain, he wrote: "Civil war is inevitable."
Starmer's spokesperson said there was "no justification" for Musk's comment.
In Whitechapel in East London, lawyer M. A. Gani, 33, said the British Bangladeshi community was "living in fear".
"We've never seen this kind of far-right groups (being so) active and (they are) anti-immigrant," he said.
"I hope that the UK (government) will take initiative to calm down the situation."
Commuters in London said protesters were intent on violence.
"I actually think the people rioting are probably puppets of people who want to stir up trouble," said Carmen Holdsworth-Delgado, a 42-year-old curator.
Interior minister Cooper told broadcasters that the government would pursue the spread of online disinformation with social media companies, and she did not accept that concerns about immigration could justify the violence.
"Reasonable people who have all those sorts of views and concerns do not pick up bricks and throw them at the police," she said.
