The Unite the Kingdom rally got underway as much smaller numbers of counter-protesters, organised by the Stand Up To Racism group, gathered under the banner of the March Against Fascism.
More than 1000 police officers were on duty to patrol the duelling demonstrations, and there was a buffer zone to keep the two from engaging with each other near the halls of government.
The marches were largely peaceful, but at one point, police said they were attacked by some members of the Unite the Kingdom march who tossed items at them and tried to break through the barriers set up to keep the two groups separate.
Officers had to use force to keep a crowd control fence from being breached, the Metropolitan Police said.
Police estimated the crowd at the Robinson rally at about 110,000 people.
The rival protest had about 5000 marchers.
At one point, the larger crowd stretched from Big Ben across the River Thames and around the corner beyond Waterloo train station, a distance of around a kilometre.
While the crowd was large, it fell far short of the one of the biggest recent marches when a pro-Palestinian rally drew an estimated 300,000 people in November 2023.
Robinson, whose real name is Stephen Yaxley-Lennon and is known for his nationalist and anti-migrant views, billed the march as a demonstration for free speech, and also said it was in defence of British heritage and culture.
The marches come at a time when the UK has been riven by debate over migrants crossing the English Channel in overcrowded inflatable boats to arrive on shore without authorisation.
Numerous anti-migrant protests were held over recent months outside hotels housing asylum-seekers following the arrest of an Ethiopian man who was later convicted of sexually assaulting a 14-year-old girl in a London suburb.
Some of those protests became violent and led to arrests.
Participants in the Unite the Kingdom march carried the St George's red-and-white flag of England and the union jack, the state flag of the United Kingdom.
They chanted: "We want our country back".
UK flags have proliferated in recent weeks across the UK — at events and on village lampposts — in what some have said is a show of national pride and others said reflects a tilt toward nationalism.
Some Robinson supporters held signs saying "stop the boats," "send them home," and "enough is enough, save our children".
At the counter-protest, the crowd held signs saying "refugees welcome" and "smash the far right".
Robinson supporters chanted crude refrains about UK Prime Minister Keir Starmer and also shouted messages of support for slain US conservative activist Charlie Kirk.
One demonstrator held a sign saying: "Freedom of speech is dead. RIP Charlie Kirk".
Robinson had planned a Unite the Kingdom rally last October, but couldn't attend after being jailed for contempt of court for violating a 2021 High Court order barring him from repeating libellous allegations against a Syrian refugee who successfully sued him.
He previously served jail time for assault and mortgage fraud.
Robinson founded the nationalist and anti-Islamist English Defence League and is one of the most influential far-right figures in Britain.
He urged followers not to wear masks, drink booze or get violent.
