LONDON — Several thousand British students protested Wednesday against government plans to triple tuition fees, two weeks after a similar demonstration sparked a small riot.College and university students across the country held marches and sit-ins to oppose the decision to increase university fees to 9,000 pounds ($14,000) a year, a key plank in the government's deficit-cutting austerity measures.In London, the university students and younger pupils in school uniforms marched from Trafalgar Square toward the Houses of Parliament, chanting "no ifs, no buts, no education cuts."Some climbed on top of bus shelters, while several attacked a parked police van, smashing the windows and scrawling graffiti.There was a heavy police presence, with hundreds of uniformed officers on duty. Police have admitted they were unprepared for violence that broke out during a November 10 protest by more than 50,000 students in London, when demonstrators stormed the building housing the headquarters of the governing Conservative Party.An 18-year-old British student pleaded guilty Wednesday to throwing a fire extinguisher off the roof of the high-rise building during that protest two weeks ago. It narrowly missed police officers standing below.Edward Woollard admitted one count of violent disorder. His lawyer said Woollard was "very sorry for his actions."District Judge Nicholas Evans said Woollard would be sentenced later. He faces a maximum of five years in prison.