UPDATE: Tommy Robinson has been released on bail, according to a post made on his personal X account.

ORIGINAL STORY: Right-wing British activist Tommy Robinson has reportedly been detained by law enforcement in London following his large patriotic-themed rally on Saturday that drew tens of thousands of people to central London.

Robinson's social media account claims he was allegedly apprehended under the "Terrorism Act 2000," though it is unclear if he is facing any charges or has been charged. Local media reports that he may have been detained for allegedly being in contempt of court over a documentary film that was screened at his rally.

The film aired Robinson's allegations over a Syrian migrant who had sued him successfully for defamation. The 2021 civil lawsuit ended with Robinson, real name Stephen Yaxley Lennon, being ordered to pay damages against the complainant and to not repeat the defamatory claims.

On Sunday, a group of Robinson's supporters gathered outside Downing Street and Scotland Yard, the police headquarters, where they demanded his release.

"Free Tommy now! Free Tommy now!" the group of about a hundred people shouted.

The London Metropolitan Police released a statement saying it was not involved in Robinson's alleged detainment or arrest.

"Met officers are not involved in the alleged arrest of Tommy Robinson and we are not aware of any links with the demonstration held yesterday in London," the department wrote on X. "This matter involves another force and we hope that further information will be released soon."

A post issued from an admin on Robinson's X account alleged that he was arrested under the "Terrorism Act 2000" act for reportedly being "someone who 'appears to be' a person who has been concerned in the preparation of acts of terrorism."

No law enforcement agency has confirmed Robinson's arrest. 

Robinson's X account posted a link to his affiliated news site Urban Scoop on Sunday night of a transcript of a phone call Robinson allegedly had with family after being detained.

"If I do not answer their [police] questions I am breaking the law," the transcript reads. "They then told me I have to give them the pin code to my phone [so they can access it]."

Robinson allegedly said: "It’s mental. You want to download my phone so you can try to find anything, that’s what you’re trying to do. Not just that, even if you’re not trying to find anything, you want to know what I’m up to. They asked me so many questions about our event yesterday."

This comes one day after Robinson held a patriotic-themed rally in the heart of London's Trafalgar Square on Saturday. An estimated 20,000 people attended the event, which screened his documentary film, "Silenced." A counter-protest group of socialists, leftists and antifa activists were kept away by police.

Supporters gather outside Downing Street demanding the release of Tommy Robinson. Photo by Andy Ngo.

This is a developing story.