
Scotland Yard says three police officers have been hurt and one has a serious neck injury. Protesters who had forced their way into Parliament Square pressed against police lines and threw missiles.
Riot police are lined up behind metal barriers surrounding the Houses of Parliament. The London Ambulance Service says 19 people have been treated for injuries - six have been taken to hospital.
There were clashes as protesters - some throwing missiles - fought to break through police lines. The police now say they are containing protesters on the square. Seven people have been arrested and a container is on fire.
The Metropolitan Police say there have been attacks using "flares, sticks, snooker balls and paint balls". Students from around the UK gathered in London for a day of protests and a rally - with police expecting about 20,000 demonstrators.
Inside the House of Commons, Business Secretary Vince Cable told MPs the fee plans were fair and would maintain the quality of universities. The coalition government is facing its first major backbench rebellion in the votes - which are expected to be taken from 1715 GMT.
It is expected that more than a dozen Liberal Democrat MPs will not support the government - including the party's deputy leader Simon Hughes. Lib Dem MP Mike Crockart has resigned his post as a ministerial aide because he intends to vote against the changes.