Protesters and police officers have been taken to hospital with minor injuries after trouble flared at a mass demonstration against tuition fees in London.
The Metropolitan police says a number have people have been arrested.
Both demonstrators and police officers suffered minor injuries during the clashes which broke out early on Wednesday afternoon during the student protest.
Hundreds of people were evacuated from the building which houses the Tory Party HQ when trouble flared.
Windows were smashed and fires started. Placards and banners were being burnt, to cheers from the crowd.
One eyewitness who works at Millbank Tower but did not want to be named said: “The fire alarm went off and every one was evacuated from the building. There are hundreds of students outside.
“We were told that it was a false fire alarm because students were throwing smoke bombs into the building.”
Thames House, the MI5 headquarters close to Millbank Tower, was sealed with heavy metal doors and police were guarding the rear exits.
This is only the beginning of the resistance to the destruction of our education system and public services. Protesters’ statement
Dozens of protesters climbed onto the roof of the building next to Millbank Tower. One worker said individual floors were taking the decision to send staff home early.
The protesters in the Tory HQ building and on the roof released a statement which said: “We oppose all cuts and we stand in solidarity with public sector workers, and all poor, disabled, elderly and working people.
“We are occupying the roof in opposition to the marketisation of education pushed through by the coalition government, and the system they are pushing through of helping the rich and attacking the poor.
“We call for direct action to oppose these cuts. This is only the beginning of the resistance to the destruction of our education system and public services.”
It is estimated around 30,000 students and lecturers were protesting.
As Nick Clegg stood in for David Cameron at Prime Minister’s Questions, students warned they will attempt to oust Liberal Democrat MPs who vote for a tuition fee hike.
We should be clear that the Government has asked students to pay three times as much for a quality that is likely to be no better than what they are receiving now and perhaps worse. Aaron Porter, NUS President
Aaron Porter, president of the National Union of Students (NUS), said they will attempt to force a by-election in the constituencies of MPs who renege on a pre-election pledge to oppose any hike.
Speaking ahead of the protest, Mr Porter said: “We will initiate a right to recall against any MP that breaks their pledge on tuition fees.”
He said that swingeing cuts to university teaching budgets laid the groundwork to justify trebling fees.
But Mr Porter added: “We should be clear that the Government has asked students to pay three times as much for a quality that is likely to be no better than what they are receiving now and perhaps worse.”
The coalition agreement, drawn up between the Tories and the Lib Dems, said they would bring forward legislation to “introduce a power of recall, allowing voters to force a by-election where an MP is found to have engaged in serious wrongdoing and having had a petition calling for a by-election signed by 10 per cent of his or her constituents.”
It is understood that this proposal is not yet going through Parliament.
Nick Clegg came under attack for his u-turn over increasing tuition fees at Prime Minister’s questions.
But he insisted the Government’s plans to charge up to £9,000 a year in fees from 2012 was a “fair and progressive solution to a very difficult problem”.
In response to Labour’s deputy leader Harriet Harman, he said: “The proposals we have put forward will mean that those who earn the least will pay much less than they do at the moment, those who earn the most will pay over the odds to provide a subsidy to allow people from poor backgrounds to go to university.”
Ms Harman said Mr Clegg had been “led astray” by the Conservatives during the negotiations to form the coalition Government.
Universities Minister David Willetts told Channel 4 News the following measures are being taken to help students:
The system we will introduce takes people's different circumstances into account.
No eligible student will be expected to pay tuition charges upfront. They will be able to apply for loans - including, at last, part-time students.
We will introduce a £150 million national scholarships programme. This will include different kinds of support, including a free first year for students from the most disadvantaged backgrounds, and a foundation year for young people with high potential but lacking qualifications.
We will also introduce a more generous student support package that's linked to family income.
Graduates will not need to repay their loans until they earn £21,000 (increased from the current £15,000). If your salary falls beneath £21,000, repayments will stop.
For graduates earning under £21,000, the real interest rate will be zero - as now.
Graduates who earn more will repay their loans at a higher rate of interest.
If, after 30 years, a graduate has not paid off all of his or her loans, the remainder will be written off.