Thousands of supporters of jailed far-right agitator Tommy Robinson marched in London on Saturday demanding his release with police deployed to keep them apart from a large counter-protest.

Robinson, 42, is serving an 18-month jail term in London's Belmarsh prison, imposed in October after he admitted breaching a 2021 High Court injunction.

Protestors organised under the name "Stop the Isolation" and "Unite the Kingdom" gathered outside Waterloo railway station before heading towards parliament.

Many waved England flags, with one reading "stop the boats", while others wore red hats carrying the initials MEGA (Make England Great Again), a variation on US President Donald Trump's campaign slogan. 

"Tommy Robinson shouldn't be in prison, he is a political prisoner," protester Liz, 55, from Birmingham in central England, told AFP.

"This country needs someone like Trump. He is strong, he is getting rid of illegals," she added.

Some protesters held placards reading "end state-sanctioned persecution", "Free Tommy" and "UK, stop the rape of white children", in reference to a gang scandal in which thousands of girls around the country were sexually abused.

The issue recently resurfaced when X owner Elon Musk made incendiary comments after the Labour government resisted calls to hold a national inquiry into the scandal. He also  reposted several comments calling for the release of Robinson, whose real name is Stephen Yaxley-Lennon.

Demonstrator Craig, 50, who held up a T-shirt reading "thank you Elon Musk", told AFP that "the UK justice system is corrupt". 

"Elon Musk has been speaking for us, he is a great help," he added.

The crowds sang Robinson's name, along with "Rule Britannia", as they started the march towards the prime minister's residence in Downing Street.

A large counter-protest organised by Stand Up To Racism was to march to Trafalgar Square, close to the final gathering point of the main demonstration.

Officers were deployed to keep the groups apart.

A leading figure in Britain's increasingly visible far-right scene, with around a million followers on the X social media platform, Robinson was prominent online throughout the anti-immigrant unrest that rocked the country last year.

Robinson first shot to prominence in 2009 when he helped found the now-defunct English Defence League (EDL) in his hometown of Luton, north of London.

His adopted name belonged to an infamous football hooligan and many EDL members were thought to be linked to hooligan gangs.