Police officers have been injured and protesters arrested during demonstrations against tuition fees. MPs have voted to increase the cap on student fees to £9,000 in England.
Trouble started when a small group of protesters tried to break through police lines in Parliament Square.
One police officer has been taken to hospital with a serious neck injury while another has a leg injury.
Several protesters were seen being led away with their arms being held by officers in riot gear.
London Ambulance said it had treated six people for injuries.
People have come to London with the intention of committing violent disorder. Met Police
Protesters hurled flares, sticks, snooker balls and paint balls at officers as they attempted to break through metal barriers.
Wooden benches in Parliament Square were set on fire, and two demonstrators were seen standing on top of the bonfire, watched by cheering protesters.
Speaking outside New Scotland Yard, Superintendent Julia Pendry said: “The Met is extremely disappointed with the behaviour of protesters.
“It is absolutely obvious that people have come to London with the intention of committing violent disorder, not coming for peaceful protest.
“That can be proved by the fact they have deviated from the agreed route. There has been seven arrests and three officers injured and they are in hospital. Obviously there has been a continued unprovoked attack by protesters.
“Unfortunately what is happening now is we are using a number of tactics, including containment, in Parliament Square.
“Those who are vulnerable and have committed no offences may leave Parliament Square if they go via Whitehall.”
Speaking about her colleagues, she added: “They came to work this morning to facilitate peaceful protest and end up being attacked by missiles, flares and other objects.”
Lib Dem MP Michael Crockart has resigned as a parliamentary aide to Scottish Secretary Michael Moore.
Meanwhile our political correspondent Cathy Newman says she has heard that Jenny Willott, Lib Dem MP for Cardiff Central and Parliamentary Private Secretary (PPS) to Chris Huhne has joined Mike Crockart and resigned over the tuition fees issue.
Follow the Channel 4 News live blog: Tuition fees vote
My earlier predictions that today's protest would absolutely lead to violence on a wider scale then we have seen have, it seems, been entirely borne out by events writes Chief Correspondent Alex Thomson.
We witnessed a police officer knocked to the ground and injured before the protest had moved a mile from London University early this afternoon.
From the outset the mood today was different. Radically different.
Read more: tuition fees protest turns violent
In the Commons, Business Secretary Vince Cable said the Coalition Government’s plans to increase fees from £3,290 a year to up to £9,000 were “progressive”.
He added: “We could have made a decision to drastically cut the number of university students, we could have cut student maintenance, we could have cut the funding to universities without replacing it.
“But instead we have opted for a set of policies that provides a strong base for university funding, which makes a major contribution to reducing the deficit and introducing a significantly more progressive system of graduate payments than we inherited. I am proud to put forward that measure to this House.”
Lib Dem Deputy Leader Simon Hughes, who is planning to abstain or vote against in today’s vote, asked Mr Cable how he could guarantee that universities did not charge as much as they could.
He said any university charging more than £6,000 a year would have to satisfy a test to ensure that children from poorer families were protected.
Shadow Business Secretary John Denham said Labour had introduced top-up fees to give universities more money, not to replace cash being taken away by the Government.
He argued that if the university budget was only being to the same extent as other departments, rather than 80 per cent, fees would only have to rise by “a few hundred pounds”.
Mr Denham added: “The vote technically today is on a very narrow issue: the fee cap. But behind it is the most profound change in university funding since the university grants committee was set up in the 1920s. It is the ending of funding for most university degrees. It is a huge burden of debt on graduates. It is an untried, untested and unstable market for students.”
I would feel ashamed if I didn’t deal with the way that the world is
Lib Dem leader Nick Clegg
Earlier, Lib Dem Leader Nick Clegg was asked if he would feel ashamed when he votes for higher fees. He said: “No, I would feel ashamed if I didn’t deal with the way that the world is, not simply dream of the way the world I would like it to be.
“In the circumstances which we face, where there isn’t very much money around, where many millions of other people are being asked to make sacrifices, where many young people in the future want to go to university – we have to find the solution for all of that.”