A UK judge on Monday jailed far-right agitator Tommy Robinson for 18 months after he admitted committing contempt of court over a long-running libel case involving a Syrian refugee.

The sentence is the latest jail term for one of Britain's most prominent anti-Muslim activists, who is blamed for helping fuel anti-immigration riots earlier this year.

It came after Robinson -- whose real name is Stephen Yaxley-Lennon -- pleaded guilty earlier on Monday to 10 breaches of a 2021 High Court order.

It bars the 41-year-old far-right figurehead from repeating false allegations he had made about the Syrian refugee, who successfully sued him for libel.

Handing down the 18-month jail sentence at Woolwich Crown Court in southeast London, judge Jeremy Johnson said Robinson's actions were a "planned, deliberate, direct, flagrant breach of the court's orders".

"Nobody is above the law. Nobody can pick and choose which injunctions they obey and those they do not," the judge added.

"It is in the interests of the whole community that injunctions are obeyed."

Robinson, wearing a grey suit and waistcoat with no tie, was held in custody, as some of his supporters looked on in court.

He had 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.

Lawyers for the Solicitor General, a senior government post advising on legal matters and which pursues such cases, said during the hearing that Robinson had been "thumbing his nose at the court".

It accused him of "undermining" the rule of law, including by last year helping to publish a film called "Silenced", which contains the libellous allegations.

The film remains pinned to the top of Robinson's profile on the social media site X.

The former football hooligan, who helped form the now-defunct far-right English Defence League in 2009, had landed himself back in court because of his "principles", his lawyers argued.

Robinson, who brands himself as a free speech advocate, has previously served time for contempt of court, which is not a crime but can be sanctioned with a jail term.

He also has several criminal convictions, including for assault.

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

Robinson, 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.

He was widely condemned for a stream of social media posts during the week of violence, which was sparked by false rumours 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. (AFP)