Placards and chants carried messages such as “Send them home” and “We want our country back.” Children were also seen among the attendees.
The rally followed a summer of unrest, including repeated protests outside hotels housing asylum seekers.
The UK is currently facing record migration levels, with over 28,000 migrants having crossed the English Channel so far this year, making immigration the central political issue in the country, overtaking economic concerns.
Tommy Robinson, whose real name is Stephen Yaxley-Lennon, told the crowd: “Today is the spark of a cultural revolution in Great Britain. This is our moment. We’ve shown there is a tidal wave of patriotism ready to rise.”
Adding fuel to the political fire, billionaire entrepreneur Elon Musk made a surprise appearance via video link, voicing support for Robinson’s movement and sharply criticizing the UK government.
“I want Britain to be greater than it ever has been. There’s something beautiful about being British,” Musk said.
“What I see is a destruction of Britain, initially a slow erosion, but now a rapid one, through massive, uncontrolled migration and a failure of government to protect its own people, including children who are being gang raped,” he added.
Musk also said: “This has got to stop. The people need to be in charge, not a detached bureaucracy. There needs to be massive reform.”
Meanwhile, a smaller counter-protest of around 5,000 people, organised by Stand Up to Racism, assembled nearby, calling for tolerance and unity.
“The idea of hate is dividing us, the more that we welcome people, the stronger we are as a country,” Ben Hetchin, a teacher at the demonstration, told Reuters.
Authorities said further arrests are expected as investigations continue.