London ? Furious student protesters attacked a car carrying Prince Charles and his wife, Camilla, vandalized buildings and battled riot police Thursday as a controversial increase in university fees triggered Britain’s worst political violence in years.

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. 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!”

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 thumbs 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.

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

Prime Minister David Cameron said the violence against the royal couple was “shocking and regrettable.”

“It is clear that a minority of protesters came determined to provoke violence, attack the police and cause as much damage to property as possible,” Cameron said. “They must face the full force of the law.”

Police said it was unclear whether the royals had been deliberately targeted, or were simply in the wrong place at the wrong time.