Notorious UK far-right agitator Stephen Yaxley-Lennon, known by the pseudonym Tommy Robinson, was given an 18-month jail sentence after he admitted on Monday committing contempt of court over a long-running libel case involving a Syrian refugee.

Yaxley-Lennon, one of Britain's most prominent anti-Muslim activists and blamed for helping fuel anti-immigration riots earlier this year, pleaded guilty to breaching a 2021 High Court order against him. It had barred the 41-year-old from repeating false allegations he had made about the Syrian refugee, who successfully sued him for libel.

Yaxley-Lennon, who helped form the now-defunct far-right English Defence League in 2009, was accused of "knowingly" breaching the order on multiple occasions. 

Lawyers have previously said that included Yaxley-Lennon having "published, caused, authorized or procured" a film entitled Silenced which contained the libelous allegations. The film, which has been viewed millions of times and was played in London's Trafalgar Square in July, remains pinned to the top of Yaxley-Lennon's profile on the social media site X. 

On Saturday, thousands of his supporters and other protesters marched through central London demanding his release, as well as tougher immigration laws.

Yaxley-Lennon appeared Monday at Woolwich Crown Court in southeast London, wearing a gray suit and waistcoat with no tie. He turned himself in to police on Friday, after an arrest warrant was issued following his failure to appear for a July court hearing on the case.

Sentencing Yaxley-Lennon, Judge Jeremy Johnson said: "The breaches were not accidental or negligent or merely reckless. Each breach of the injunction was a considered and planned and deliberate and direct and flagrant breach of the court's order."

Aidan Eardley, a lawyer representing the Solicitor General, said Yaxley-Lennon had been found in contempt on three separate occasions and was jailed for it in 2019. He also has several criminal convictions, including for assault.

Yaxley-Lennon's lawyer Sasha Wass said: "He acted in the way that he did, and he accepts his culpability, because he passionately believes in free speech, a free press and the overwhelming desire that he has to expose the truth."

Wass also said that Silenced had been "effectively commissioned" through U.S. conspiracy theorist Alex Jones' Infowars company.

Yaxley-Lennon was sentenced to 18 months, less three days spent in custody after he was arrested on Friday. The judge said that four months could be removed from Yaxley-Lennon's 18-month sentence if he tried to "purge" his contempt, including by taking down copies of Silenced.

The judge said of Yaxley-Lennon that "all his actions so far suggest that he regards himself as being above the law".

Yaxley-Lennon, who has reportedly spent recent months outside the UK, has amassed a large online following built around his vehemently anti-Muslim, anti-immigrant messaging. Demonstrators at anti-immigrant riots which erupted across England and Northern Ireland in late July and early August could be heard chanting his name.

Yaxley-Lennon was widely condemned for a stream of social media posts during the week of violence, which was sparked by false rumors that the suspect behind the fatal stabbings of three young girls was a Muslim asylum seeker.

He has been a familiar sight at far-right rallies over the years, but has seen his profile grow over the last year after his X account was reinstated following billionaire Elon Musk's purchase of the platform.