Right-wing, anti-immigrant protesters and opposing anti-racism demonstrators began large rallies in London on Saturday, closely watched by a beefed up police operation aimed at heading off any clashes between the rival gatherings.

A few thousand joined the "Unite the Kingdom" march organised by anti-immigrant and anti-Muslim activist Stephen Yaxley-Lennon, known by the pseudonym Tommy Robinson, with the march heading towards parliament, carrying English and British flags, and banners reading "When will the government act for the British public?". But they now worry the effect of climate change on Iceland's glaciers could hasten and intensify that next volcanic event.

Meanwhile a counter protest of anti-racism campaigners and trade unionists also gathered, carrying banners saying "refugees welcome" and "smash the far right".

Deputy Assistant Commissioner Rachel Williams, who is leading a policing operation that drafted in officers from around the country, said they were well prepared.

"We will have significant resources in place to respond to any incidents, to deal decisively with any offences, and to keep disruption to other members of the public and businesses to a minimum," she said on Friday.Britain saw days of rioting in towns and cities across the country at the end of July in the wake of the murder of three young girls at a dance workshop in Southport, after misinformation on social media wrongly identified the suspected killer as a Muslim migrant.

The unrest, which Prime Minister Keir Starmer described as racist and blamed on far-right thuggery, targeted hotels housing asylum seekers and mosques. It ended after police made more than 1,500 arrests and charged about 1,000 people.

The right-wing protesters describe themselves as "patriots", who say Britain is under threat from migrants and Islamification. Their critics, including most lawmakers, say their number includes racists, far-right supporters and soccer hooligans bent on violence.

Yaxley-Lennon, who was accused by some media and politicians of enflaming tensions which led to the riots, was not present at the march as he is being held in police custody ahead of a contempt of court case to be heard on Monday.

On Friday, he was also charged under terrorism laws with failing to provide his mobile phone PIN code when he left Britain in July.

"We do not care if you are black, brown, white or green, what we care about are shared values, our culture, and the direction of our nation," a message on his X account said.

The protests come as official figures on Saturday showed the number of asylum seekers crossing the Channel this year from Europe in small boats - an issue that has angered many in Britain - hit 29,578, more than for the whole of 2023.