Hundreds of demonstrators descended on the capital on Saturday afternoon, blocking off the road around Trafalgar Square.
Bottles, metal barriers and other objects were hurled at officers, five of whom suffered minor injuries, police said.
Nine men were arrested during the protest as supporters chanted "Free Tommy Robinson".
Derek White, 46, from Bournemouth, in Dorset, was charged with possession of a knuckleduster and is due to appear at Westminster Magistrates' Court on Monday.
A 50-year-old man arrested for possession of a flare was released under investigation, along with another man held for possession of cannabis and breach of the peace.
Six other men arrested for public order offences have also been released under investigation.
The Metropolitan Police said officers are gathering CCTV from the area as the investigation continues.
The protest was the latest in support of Robinson, who was jailed for contempt of court for using social media to broadcast details of a trial which is subject to blanket reporting restrictions.
Leeds Crown Court heard how he 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.