Fourteen people - seven of them police officers - have received minor injuries during a march in London against plans to treble British university tuition fees.
Some protesting students broke into a building where the governing Conservative Party has its headquarters and smashed windows.
Scotland Yard says the vast majority of demonstrators were peaceful, and student leaders have condemned the violence.
Tens of thousands of students and lecturers were protesting against government proposals under which the maximum cost of courses will nearly treble to as much as £9000 a year.
The National Union of Students says it will attempt to force by-elections in the constituencies of MPs who go back on pledges to oppose fee increases.
However, there is no legislation currently in place to require this.
The coalition government is cutting higher education funding in England by 40% as part of auserity measures.