The officers tore down pop-up tents and arrested people who had tried to set up a tent city in Trafalgar Square.
At 1.30pm around 25 tents were pitched next to Nelson’s Column after 200 protesters broke free from the main march, which was protesting about education spending cuts and the rise in university tuition fees.
Police said they had broken section 12 of the Public Order Act by leaving the official protest route.
Most protesters left to rejoin the main march before around 100 police officers arrived at the scene at 2.45pm.
They set up a loudspeaker and demanded that the protesters leave or face arrest before moving in and carrying the demonstrators away by 3.15pm.
The 10,000-strong crowd of protesters on the main march included Pulp singer Jarvis Cocker, 48, and model and actress Lily Cole, 22.
Demonstrators carried placards saying “Scrap Tuition Fees” through the streets and chanted: “No ifs, no buts, no education cuts”.
Around 200 hooded and masked protesters broke through police to gather near the stock exchange but undercover police, also in hooded tops, were there to make speedy arrests.
Many marchers complained about the number of police on the streets.
Tom Harris, a 20-year-old student at Royal Holloway University said: “There are too many here. There were police on horses going up and down constantly.
“Rows of police were pushing people back if they asked them questions. They were being aggressive for no reason.”
Eighty-nine-year-old Chaine Rosenberg from North London said she marched because people of all generations would be affected by the cuts.
She said: “They are really hitting poorer people, not the bankers at all.”
Rosenberg added: “The police seem to be making the law tougher for younger people, making it difficult to protest.”
Last night, 24 arrests were made in connection with the march.
