Several officers were punched, kicked and struck by bottles tossed by people at the fringes of the Unite the Kingdom rally, Metropolitan Police said.
There were nine arrests, with many more likely, the force said, as violence flared at the protest, which featured a video cameo appearance from Tesla and X owner Elon Musk.
Police estimated that Robinson drew about 110,000 people, while the rival March Against Fascism protest organised by Stand Up To Racism had about 5000 marchers.
More than 1600 officers were deployed in total across the city, with 500 brought in from other forces, the Metropolitan Police said.
"We continue to see significant aggression directed at officers by Unite the Kingdom protesters," police posted on the X platform.
The marches had been largely peaceful.
But toward the late afternoon, Unite the Kingdom supporters threw items at the rival rally and tried to break through barriers set up to separate the groups.
Tesla boss Elon Musk waded into British politics, calling for a change of government.
He also railed against the "woke mind virus".
Earlier, officers had to use force to keep a crowd-control fence from being breached, the police said.
Counter-protesters heckled a man with blood pouring down his face, who was being escorted by police from the group of Robinson supporters.
It wasn't immediately clear what happened to him.
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 in 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 this summer 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 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.
With PA
