David Cameron called today for "the full force of the law" to be used against people who assaulted police or damaged property during yesterday's student demonstrations at Conservative Party HQ.
The Prime Minister said those who opposed his plans to raise the cap on university tuition fees had a right to protest but insisted that "violence and lawbreaking" must not go unpunished.
An urgent investigation was under way today into how police were caught out when violent protesters turned a demonstration against higher tuition fees into an ugly battle.
Fourteen people were injured, including seven police officers, when dozens of activists stormed the tower block housing the Tory party headquarters in Millbank, Westminster.
Tens of thousands of pounds worth of damage was caused as protesters smashed windows, damaged furniture and daubed walls with graffiti, sparking a four-hour stand-off.
Fifty-one people were arrested for offences including criminal damage and aggravated trespass and many more were photographed and identified as police prepared to scour footage for evidence of crimes. A Metropolitan Policespokesman said it is not known if anyone has been charged or how many remain in custody at police stations across central London.
Speaking during a round of TV interviews at the G20 summit in South Korean capital Seoul, Mr Cameron told Channel 5 News: "People who assault police officers or who smash windows or who break property are breaking the law and yes, those people I hope... will be prosecuted. They should be.
"People long in our history have gone to marches and held banners and made protests and made speeches and that's part of our democracy. That is right.
"What is not part of our democracy is that sort of violence and lawbreaking. It's not right. It's not acceptable and I hope that the full force of the law will be used."
Mr Cameron said that as he watched footage of the Conservative office under attack, he was worried for the safety of friends and colleagues inside.
"I was worried for the safety of people in the building because I know people who work in there, not just the Conservative Party but other offices as well," he told the BBC.
"So I was on the telephone. I wanted to know what was happening. I wanted to know that people were safe.
"And what I felt when I saw those pictures was of course people have a right to protest peacefully, but I saw pictures of people who were bent on violence and on destruction and on destroying property and that is completely unacceptable.
"And we need to make sure that that behaviour does not go unpunished and we need to make sure that we don't, as the police put it, see scenes like that on London's streets again.
"I thought it was extremely serious. I could see a line - a thin blue line - of extremely brave police officers trying to hold back a bunch of people who were intent on violence and destruction."
Mr Cameron said he agreed that police had lessons to learn on how they handled the protest.
"They were very brave, those police officers, but as the police themselves have said, there weren't enough of them and the police response needs to reflect that," said the Prime Minister.
"So I'm very glad that the Metropolitan Police Commissioner has said what he said and I think we need to learn the lessons very rapidly."
Mr Cameron insisted that the new fees structure - under which universities can charge up to £9,000 a year for tuition and graduates will pay the money back over their working lives - was "a more progressive system than the one that it will replace".
And he added: "I think the right place for the debate and argument to take place is in Parliament, is in debates rather than the scenes that we saw.
"But of course people have a right to protest and I'm sure that people will do that - as they do under all governments and as always happened in our country. But the scenes of our violence, that is not acceptable."
Metropolitan Police Commissioner Sir Paul Stephenson said the unexpected clashes were an "embarrassment to London and to us" and pledged to examine what went wrong.
He also apologised to those left inside 30 Millbank for their "traumatic experience" and said police were caught out as there was "no real history" of that level of violence during student protests.
Sir Paul added: "I think we've also got to ask ourselves some questions. This level of violence was largely unexpected and what lessons can we learn for the future. We are already doing that and asking those questions.
"Certainly I am determined to have a thorough investigation into this matter."
The violence was sparked as a peaceful march involving thousands of students mobilised from across Britain by looming fee rises passed the landmark building on the River Thames.
A small group of police and security staff were forced to retreat as a mass of people surged forward, led by a smaller group, many of whom were masked, who stormed the building and smashed windows.
An angry stand-off ensued as a handful of police officers attempted to stop more people entering the building as up to 50 protesters ran amok inside, smashing windows and hurling missiles from the seventh-floor rooftop.
One man was seen armed with a hammer while others brandished metal poles and wooden sticks used to hold placards, as others started fires and lit fireworks in the forecourt to the sound of drums and dance music.
London mayor Boris Johnson said he was appalled that a small minority "shamefully abused" their right to protest and warned that those involved with "face the full force of the law".
He said: "The Metropolitan Police Commissioner has assured me that there will be a vigorous post-incident investigation. He will also be reviewing police planning and response."
National Union of Students president Aaron Porter described the violence as "despicable" and said a minority of protesters who planned to cause trouble had "hijacked" the march.
The police inquiry is likely to focus on police preparation for the march, including the decision to categorise it as low risk and to draft in only around 225 officers to marshal more than 50,000 people.
The tactics of public order commanders once violence erupted will also come under the spotlight after officers were ordered not to intervene as protesters attacked the building.
Representatives of the police rank-and-file will want to know if senior officers did all they could to reduce the danger faced by those left to try to hold the embattled front line.
Students and staff were protesting against government plans to charge students up to £9,000 a year from 2012 - triple the current £3,290 fee.
Union leaders say the increase, along with swingeing cuts to university budgets, will mean the end of affordable higher education.
Mr Cameron denied Britain was facing a repeat of the 1980s, when unpopular cuts helped spark violent demonstrations and rioting.
He told Channel 5 News: "I think there's a very big difference to the 1980s. This time we have a coalition Government, we have two parties that have come together in the national interest that's trying to take the country with us as we do difficult things in terms of dealing with the debt and the deficit.
"I think most people understand we have to take these steps, we have to get Britain out of the danger zone.
"I think the will of the public was expressed at the time of the election when they rejected debt and deficit and putting off these difficult decisions under Labour and they chose a new approach and we've got to be true to that and stick to that.
"We'll be absolutely resolute in pursuing that path."
Mr Cameron insisted there was no question of overturning the decision on fees, telling ITV News: "We won't go back. Look, even if we wanted to, we shouldn't go back to the idea that university is free."
He denied that expected cuts in police numbers would make forces less able to deal with similar demonstrations in future.
"What the police themselves have said - and to be fair to Paul Stephenson he has himself said - is that the police response was inadequate and that the lessons have to be learned," said Mr Cameron.
"There are something like 30,000 police officers in London. There were a very small number of police officers against a very violent group of people.
"I think the police themselves have said that the problem here was about the planning, was about the intelligence, was about the resourcing of that particular operation.
"I am quite convinced that the reductions in police spending that we're making can actually be done without losing the visibility and the activity of the police officers on our streets."
Mr Porter said students had "lost a lot of public sympathy" because of the violence.
In an interview with BBC Breakfast, he said: "What we had done was assemble 50,000 students which I'm sure would have got a hell of a lot of attention and would have sent a clear message to Government.
"But if we're now having to spend time talking about the rights and wrongs of violence and criminal damage, actually in many respects I think it undermines our argument rather than allows us to concentrate on the devastation to our universities and colleges, and the issue that we could rightly point out, huge cuts to what students will be receiving."
He added: "I think we have to accept that we have lost a lot of public sympathy and actually that does undermine our case.
Cameron spells out hopes for foreign students
By Nigel Morris, Deputy Political Editor
David Cameron suggested yesterday that steep rises in tuition fees would help to prevent bigger increases in the prices charged to foreign students.
He urged Chinese youngsters not to let their fears about the expense of courses deter them from applying to British universities.
The Prime Minister’s comments, which risked further antagonising student protesters in Britain, was asked to explain the Government’s decision to allow universities to charge up to £9,000 a year in tuition fees.
Speaking at Peking University, he said the controversial increases would ensure that “our universities are well funded and we won’t go on increasing so fast the fees for overseas students.” Tuition fees for foreign students in Britain currently average £20,000 a year.
Mr Cameron said agreeing the increases for domestic students had been a tough decision for the coalition, but was crucial to help Britain compete with universities in the United States, India and China in attracting the world’s brightest students.
He added: “In the past we have been pushing up the fees on overseas students and using that as a way of keeping them down for domestic students.
“We have done the difficult thing. We have put up contributions for British students. Yes, foreign students will still pay a significant amount of money but we should now be able to keep that growth under control.”
He told the undergraduates that he was keen for Chinese people to study in Britain as the links formed could later lead to business ties between the two countries."