Tommy Robinson supporters have blocked the road outside the Old Bailey with a double decker bus.
The vehicle was transformed into a makeshift stage featuring an image of a gagged Robinson on a large screen.
The former English Defence League (EDL) founder faces fresh contempt of court proceedings at the Old Bailey today.
Mr Robinson, whose real name is Stephen Yaxley-Lennon, will face High Court judges today over allegations he committed contempt of court by filming defendants in a criminal trial and broadcasting footage on social media.
With 90 minutes to go before the two-day hearing was due to begin, around 100 people, some carrying Union flags, assembled on the closed-off road outside the historic court building.
Supporters, led by a man with a loudspeaker, chanted: “Oh, Tommy, Tommy ... Tommy, Tommy, Tommy, Tommy Robinson, along with: "We want justice, we want justice now," and "Tommy Robinson is a history maker."
The supporters are being segregated from the main walkway into the court, accessed by legal representatives and journalists, by a series of interconnected metal fences.
City of London police said the road between Limeburner Lane and the Old Bailey remained closed due to the demonstrations, adding that updates on the status of the closure would be issued throughout the morning.
Robinson shared a video of himself in a car on his way to court on Thursday morning, singing along to Bob Marley's Everything's Gonna Be Alright.
Speaking in the video to his followers on messaging app Telegram, Robinson said: "Hey Attorney General if I'm meant to be stressed and worried it's not working bro."
Robinson later arrived at court to applause and chants from his supporters, mobbing him as he made his way to the stage.
In a direct appeal to "the mainstream media", Robinson said: "It's not me on trial today - it's your freedom as journalists.
"This will he used as a test case. I have not broke any law," he added, before wishing his wife a happy birthday.
He is due to appear in court to face an allegation he committed contempt of court by filming defendants in a criminal trial and broadcasting the footage on social media.