LONDON (AFP) - Police and protesters clashed as several thousand students took to the streets of central London on Wednesday to rally against tuition fees, education cuts and debt.

Riot police tried to push back protesters who stormed the Conservative party headquarters and tore down metal barricades as they flooded into nearby Parliament Square.

London's Metropolitan Police said they arrested 11 people, for offences including assaulting police, criminal damage, and violent disorder, as hundreds of police and riot officers were deployed.

Britain's biggest student protest in four years started peacefully and in a party mood, with students marching towards the Houses of Parliament.

"Education is a right, not a commodity" read one of the placards held up by students, who are calling for free higher education and want to see tuition fees scrapped.

"Tuition fees? No way! Tax the rich and make them pay!" the students chanted as they marched.

"We want free education for everyone. It makes economic sense," said 26-year-old Nehaal Bajwa, who is paying £9,360 (S$19,150) a year to study for a master's degree in economics.

"Plenty of money goes to the banks. We want it to go into school," he said.

David, a 25-year-old German student who declined to give his surname, said: "I'm here to show solidarity.

"In Germany they scrapped the fees in some counties after massive protest. It is inspiring," he said.

Tensions mounted during the day, however, with angry crowds yelling abuse at police, throwing paint and lighting flares, many wearing black balaclavas and hoods.

"Various missiles were thrown at the officers and protesters pulled down protective fencing around the grass area in Parliament Square," the force said in a statement, adding that three officers suffered minor injuries.

Customers were trapped inside a Starbucks coffee shop after eggs and white paint were thrown at the window, with protesters railing against the company's tax policies.

A group of protesters held a sit-down protest outside London's police headquarters, New Scotland Yard, chanting slogans against police and Prime Minister David Cameron's Conservative party.

The protest was the biggest since 2010 when around 50,000 took to the streets in anger at the passage of a law to increase tuition fees in a rally that degenerated into running street battles with police.

Enrolment fees have since risen to as much as £9,000 in around a third of English universities, while Scottish universities have remained free.

Demonstration organiser Aaron Kiely said the protest marked the start of a "major wave of action" running up to next year's general election.