They Spouted Hate Online. Then They Were Arrested.

A 53-year-old woman from northwest England was jailed for 15 months after posting on Facebook that a mosque should be blown up “with the adults inside.” A 45-year-old man was sentenced to 20 months for goading his online followers to torch a hotel that houses refugees. A 55-year-old woman was questioned by the police for a viral post that wrongly identified the suspect in a deadly stabbing knife attack at a children’s dance class.

These and other people are accused of being “keyboard warriors,” in the words of one British judge, exploiting social media to stir up the anti-immigrant riots that exploded after the suspect was arrested in the fatal stabbings of three young girls at the dance class, in the town of Southport. Their cases have now become examples in a politically charged debate over the limits of free speech in Britain.

With the courts handing down harsh sentences to hundreds who took part in the violent unrest, and calls for the government to strengthen regulation of online content, some argue that the authorities risk going too far. Not only are judges locking up far-right rioters, these critics say, but they are also opening the door to a broader crackdown on speech.

The noisiest critiques have come from Elon Musk, the billionaire owner of X, once known as Twitter. After far-right groups used his platform to spread disinformation about the attack and foment the violent disorder that followed, Mr. Musk waded into the debate, claiming that civil war “is inevitable” in Britain and attacking Prime Minister Keir Starmer.

“The U.K. is turning into a police state,” Mr. Musk posted on Monday, referring to an emergency plan activated by the government to ease pressure on chronically overcrowded jails, under which defendants can be held longer in police cells until space opens in prisons.