London, England (CNN) -- At least 51 people have been arrested, authorities said Thursday, after students stormed the headquarters of Britain's ruling party to protest plans to raise tuition fees.
The students spray-painted anarchy symbols and set off flares before being forced out of the Conservative Party building in London.
They broke large windows, painted obscenities on the walls, and later climbed onto the roof and hurled objects down.
Some set fires and shot off firecrackers outside the building.
"This was thuggish behavior by criminals and we need to ensure we have a thorough post-incident investigation to bring these criminals in front of a court to answer for their crimes," said Sir Paul Stephenson, the Metropolitan police commissioner. "It's not acceptable, it's an embarrassment for London and for us, and we have to do something about that."
The violence came during a largely peaceful protest by students against government plans to allow universities to increase tuition fees. The National Union of Students said 50,000 demonstrators were on the streets.
Arrests were primarily for trespassing and causing criminal damage, London's Metropolitan Police said.
Eight people suffered minor injuries and were taken to hospitals, police said. The injured included both police and protesters.
"We didn't expect this level of violence," the commissioner said.
The president of the National Union of Students, Aaron Porter, called the scenes of violence "despicable" and blamed "rogue protesters" for undermining an otherwise peaceful demonstration.
Students and university staff are protesting government plans to allow universities to charge up to 9,000 pounds (about $14,500) per year in tuition fees -- a substantial rise from the current cap of 3,000 pounds (about $4,800).
The government wants to raise tuition fees and scrap some subsidies for university students as it tries to cut a massive budget deficit.
Defenders of the plan say that universities will not have to charge the maximum they're allowed to, but an education policy expert told CNN they will.
"What will happen is that the number of (university) places will be held down -- the government will continue to limit the number of students the universities may recruit because the government subsidizes them through a loan," said Bahram Bekhradnia, director of the Higher Education Policy Institute.
"Students will want to get into university because the best jobs go to those with university degrees," he continued.
"It seems economically sensible for the universities to charge as much as they can. It may not happen immediately but in the medium term, most universities will charge the maximum," he concluded, adding that's what happened when the maximum was last increased four years ago.
CNN's Antonia Mortensen and Joyce Joseph contributed to this report.