Yellow vest campaigner James Goddard has been arrested in central London on suspicion of a public order offence.
The arrest happened outside St James’s Park Tube station on Saturday morning.
Goddard, originally from Leicester, was taken to a central London police station.
His supporters claim he was preparing to hand himself in at Holborn police station at midday.
The Met Police said in a statement: “We can confirm that a man in his 30s was arrested at 11.42am on Saturday, 12 January outside St James’s Park Tube station on suspicion of a public order offence.
“He is currently in police custody and is being taken to a central London police station.”
The arrest happened as hundreds of protesters were gathering in London ahead of a “yellow vest” inspired anti-austerity march.
The demonstration is organised by The People’s Assembly Against Austerity, which is calling for a general election.
The group had called for a national day of action on Saturday, planning demonstrations across the country, including the capital.
It formed in December and has blocked London bridges, and confronted MPs and journalists amid public protests.
Protesters met outside the BBC’s Broadcasting House and planned to march to Trafalgar Square.
Many were wearing yellow vests with slogans such as “Britain is Broken” written on the back.
People carrying drums prepared to march and political songs were being sung.
Large trade union banners were being held up in the crowd. “Let’s show the French what we can do,” cried one protester.
France has seen weeks of nationwide anti-austerity demonstrations by the “gilets jaune”, or “yellow vest”, movement.