LONDON — British police came under intense pressure on Friday after protesters furious at a controversial hike in university fees attacked the car carrying Prince Charles and his wife, Camilla, in London.

In a major security breach, demonstrators set upon the heir to the throne's Rolls Royce as it drove through London's busy West End on its way to a theater on Thursday . A group of up to 20 struck it with fists, sticks and bottles, breaking a window and splattering the gleaming black vehicle with paint.

In the frenzy, some chanted "off with their heads!"

It was Britain's worst political violence in years.

Adnan Nazir, a 23-year-old podiatrist who was following the protesters, said Charles, 62, kept his calm, gently pushing his 63-year-old wife toward the floor to get her out of the line of fire.

"Charles got her on the floor and put his hands on her," Nazir said. "Charles was still waving and giving the thumb's up.

"It was just a surreal thing," he said. "It was completely manic."

Charles' office, Clarence House, said the royal couple was unharmed. But the attack took police completely by surprise and raises serious security questions.

Investigation into violence
The chief of the Metropolitan Police, Paul Stephenson, said the force would launch an investigation into Thursday's violence.

Stephenson also said the area had been "thoroughly recced," or investigated, just before protesters surrounded the car, according to The Daily Telegraph.

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As thousands of students were corralled by police near Parliament, some strummed guitars and sang Beatles songs — but others hurled chunks of paving stones at police and smashed windows in a government building.

Another group ran riot through the busy shopping streets of London's West End, smashing store windows and setting fire to a giant Christmas tree in Trafalgar Square.

Police condemned the "wanton vandalism." They said 43 protesters and 12 officers had been injured, while 22 people were arrested. Police said the number of arrests would likely rise.

Home Secretary Theresa May said that "what we are seeing in London tonight, the wanton vandalism, smashing of windows, has nothing to do with peaceful protest."

The violence overshadowed the tuition vote, a crucial test for governing Conservative-Liberal Democrat coalition, and for the government's austerity plans to reduce Britain's budget deficit.

It was approved 323-302 in the House of Commons, a close vote given the government's 84-seat majority.

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Many in the thousands-strong crowd outside booed and chanted "shame" when they heard the result of the vote, and pressed against metal barriers and lines of riot police penning them in.

Earlier small groups of protesters threw flares, billiard balls and paint bombs, and officers, some on horses, rushed to reinforce the security cordon.

World Blog: A non-royal account of student violence in London's capital

Education is not for sale'
The scuffles broke out after students marched through central London and converged on Parliament Square, waving placards and chanting "education is not for sale" to cap weeks of nationwide protests aimed at pressuring lawmakers to reverse course.

The vote put Deputy Prime Minister Nick Clegg and his Liberal Democrat party in an awkward spot. Liberal Democrats signed a pre-election pledge to oppose any such tuition hike, and reserved the right to abstain in the vote even though they are part of the governing coalition proposing the change.

Those protesting were particularly incensed by the broken pledge from Clegg's party.

"I'm here because the Liberal Democrats broke their promise," said 19-year-old Kings College student Shivan David. "I don't think education should be free but I do think that tripling fees doesn't make any sense. We are paying more for less."

Clegg defended the proposals, saying the plans represent the "best possible choice" at a time of economic uncertainty.

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But under intense political pressure, 21 Liberal Democrat lawmakers — more than a third of the total — voted against the fee hike. Another eight, including at least one government minister, abstained.

Experts warned that fallout from the policy could pose a greater risk after the vote.

"The real danger for the government is not that they won't pass it through, but that it will be a policy fiasco," said Patrick Dunleavy, a political science professor at the London School of Economics. "By picking this fight with the student body ... the government seems to have gotten itself into choppy water."

Cameron's government describes the move as a painful necessity to deal with a record budget deficit and a sputtering economy. To balance its books, the U.K. passed a four-year package of spending cuts worth 81 billion pounds, which will eliminate hundreds of thousands of public sector jobs and cut or curtail hundreds of government programs.