Far-right activist Tommy Robinson has been taken into custody ahead of a major demonstration by his supporters in London this weekend.
Kent Police said a 41-year-old man had been arrested at the direction of the High Court and would appear at Woolwich Crown Court on Monday in connection with contempt of court allegations.
The force said Robinson has also been charged under his real name of Stephen Yaxley-Lennon with allegedly refusing to provide his phone’s PIN to officers who had stopped and questioned him at the border in Folkestone in July.
He was granted bail over that allegation and will appear at Westminster Magistrates' Court on 13 November.
The alleged offence under the Terrorism Act is not an accusation that he was planning an attack and relates solely to police powers to examine phones at ports as part of investigations.
Yaxley-Lennon is facing potential jail at Monday's hearing on contempt of court charges.
It is alleged he breached an injunction not to repeat lies about a Syrian refugee which had been previously ruled by a judge to be defamatory.
Shortly after he entered Folkestone police station on Friday afternoon, the official Tommy Robinson X account confirmed that he had been taken into custody.
The move to detain Yaxley-Lennon comes less than 24 hours before a major policing operation to contain a protect gathering potentially thousands of his supporters.
For weeks, and posting from abroad, he had been urging them to come to London on Saturday, claiming that the state was trying to silence him for speaking out about the impact of immigrants on the UK.
Metropolitan Police commanders have put in place a significant operation to contain the protest and separate it from a counter-demonstration.
Both the Met and British Transport Police are due to be supported by officers from other forces across the country. The Met said there would be a "significant police presence" to ensure the two groups were kept apart.
It is not clear how many people will attend but a similar gathering in London in July saw thousands of Robinson supporters in Trafalgar Square.
The activist, who founded the now-defunct English Defence League, has been accused by critics of whipping up tensions during the summer’s riots.
Yaxley-Lennon has not been charged with any offences relating to the disturbances.