Police arrested 11 people after thousands of students marched through London protesting against education cuts, tuition fees and student debt.
Police say two of the arrests - a man and a woman - were made after a wheelie bin was allegedly pushed at police guarding the entrance to the nearby Tory headquarters in Westminster.
The 'Free Education' march was called to oppose tuition fees of up to £9,000. It was not endorsed by the National Union of Students, whose central London office was vandalised with graffiti, including the word "scabs".
Demonstrators continued marching through central London chanting slogans such as "books not bombs" and carried banners saying "free education, tax the rich".
However, the march was largely peaceful and ended with a rally in Parliament Square. After that protesters broke through barriers to gain entry and clashed with police.
Police say the arrests include two for assaults on police officers, one for criminal damage and possession of an offensive weapon and another for violent disorder.
Three police officers were treated for minor injuries.
A police spokesman said: "Various missiles were thrown at the officers and protesters pulled down protective fencing around the grass area in Parliament Square."