Five people have been arrested during a violent protest that saw crowds of Tommy Robinson supporters in a tense stand-off with riot police.
Hundreds of far-right demonstrators descended on the capital on Saturday afternoon, occupying the road around Trafalgar Square.
The protest is the latest in what appears to be a bid to secure the former English Defence League (EDL) leader's release from jail.
Supporters chanted "Free Tommy Robinson" and hurled missiles and smoke bombs at police. Right-wing Dutch politician Geert Wilders also delivered a speech.
Scotland Yard said two people were arrested for assaulting a police officer, and three others were detained on separate charges of possession of an offensive weapon, possession of a flare and criminal damage to a bus.
The Metropolitan Police said in a statement: "During the protest there were scenes of violence which saw bottles, metal barriers and other objects thrown at officers.
"Five officers have reported injuries, which are not serious.
"The Met will now launch a post investigation collating the CCTV in the area."
Hundreds of supporters crowded on to an open-top Megabus sightseeing vehicle waving Union Jack flags, while one supporter posed on the roof in a Donald Trump mask.
By 6pm, officers had removed protesters from the bus and had kettled many of the remaining protesters on the traffic island overhead.
Other Robinson supporters crowded on to the steps of Nelson's Column and continued to chant slogans.
A spokeswoman for megasightseeing.com said: "Our London sightseeing bus was on its normal route when it got caught up in the demonstrations.
"The bus was stormed by demonstrators and the driver and a small number of customers got off.
"The demonstrators have caused a significant amount of damage to the bus which meant it had to be towed away.
"We have reported this to the police and will help them with any investigations."
Videos posted on social media appeared to show police being significantly outnumbered by demonstrators.
The Metropolitan Police have not yet responded to requests for comment about the protest.
Saturday's protest was the second in as many weeks.
Robinson was jailed for contempt of court after he used social media to broadcast details of a trial which is subject to blanket reporting restrictions.
Leeds Crown Court heard how Robinson filmed himself and people involved in the case, in footage that was watched around 250,000 times within hours of being posted on Facebook.
Robinson, who was listed by his real name Stephen Christopher Yaxley-Lennon on court documents, was sentenced to 13 months in jail on the same day as his arrest.
He was given 10 months in jail for contempt of court, and an additional three months for beaching a previous suspended sentence.
Additional reporting by PA