UK leader Keir Starmer has warned far-right protesters that they will “regret” participating in the country’s worst rioting in 13 years.

The unrest, linked to the murder of three children earlier this week, has spread across England, with anti-immigration demonstrators clashing with police and causing destruction.

In a TV address, Starmer condemned the “far-right thuggery” and promised to bring perpetrators to justice.

He guaranteed that those involved in the disorder, either directly or indirectly, would face consequences.

The riots were sparked by misinformation about the mass stabbing in Southport, which claimed the lives of three children.

False rumours about the suspect’s background have fueled the violence, which has targeted asylum seekers, mosques, and Islamic places of worship.

Police have arrested over 150 people since Saturday, and officers have been injured in clashes with rioters.

Religious leaders have issued a joint appeal for calm, and the UK interior ministry has offered emergency security to Islamic places of worship.

The violence is a major challenge for Starmer, who was elected just a month ago.

He has vowed to take action against those responsible and to address the underlying issues driving the unrest.

The rallies have been advertised on far-right social media channels under the banner “Enough is enough”.

Participants have waved English and British flags while chanting slogans like “Stop the boats” — a reference to irregular migrants crossing the Channel to Britain from France.

Anti-fascist demonstrators have held counter-rallies in many cities, including Leeds where they shouted, “Nazi scum off our streets”, as the far-right protesters chanted, “You’re not English any more”.

Not all the gatherings have turned violent. A peaceful one in Aldershot, southern England, on Sunday saw participants hold placards that read “Stop the invasion” and “We’re not far right, we’re just right”.

“People are fed up with being told you should be ashamed if you’re white and working class but I’m proud white working class,” 41-year-old Karina, who did not give her surname, told AFP in Nottingham on Saturday.

Commentators have suggested that the demonstrators may feel emboldened by the political ascendancy of anti-immigration elements in British politics.

At last month’s election, the Reform UK party led by Brexit cheerleader Nigel Farage captured 14 percent of the vote — one of the largest vote shares for a far-right British party.

Carla Denyer, co-leader of the left-wing Green party, said the unrest should be “a wake-up call to all politicians who have actively promoted or given in” to anti-immigration rhetoric.