The mood was angrier than it was last time, as thousands of demonstrators seized their final opportunity to persuade MPs to scrap plans for an increase in tuition fees.
One sixth-former talked of violence being acceptable "if that's what it takes to make our mark".
They laid siege to the House of Commons in a determined attempt to storm the seat of government. Thwarted, they turned their anger on the nearby Treasury building in Whitehall – bombarding it with missiles, including flares, sticks and snooker balls.
One estimate put the number of protesters at more than 30,000.
There were prolonged clashes, as protesters seeking to storm the Commons fought to break police lines.
Earlier, mounted police had charged protesters and thousands were contained in "kettles" outside Parliament.
The day had started peacefully but, whereas last week's march had a mischievous air to it as protesters led police a merry dance in the snow, yesterday there was a determined and purposeful atmosphere as thousands set off from the University of London.
They had been allowed to march through Trafalgar Square and down towards Buckingham Palace, before turning to head for the Houses of Parliament as MPs debated the issue.
There the march halted as police and stewards alike tried unsuccessfully to direct it up Whitehall.
The crowds, only "vaguely" under the stewards' control, according to eye-witnesses, just refused to comply.
Barriers had been erected by police, stopping protesters crossing the road in front of Parliament and getting on to the grass in the centre of the square. But protesters tore them down and bonfires were soon burning under the shadow of Winston Churchill's statue. It was then daubed with graffiti, saying: "Fuck police", "Clegg eat shit" and "Education for the masses". As it became clear it was impossible to break through police lines, protesters turned their attention to the Victoria Street entrance to the square, where lines of police had blocked the road. They again started throwing missiles and, after a lot of pushing and shoving, mounted police were sent in.
"I was terrified. My heart was pounding when the horses came towards me," said one student who refused to be named.
Julyan Phillips, 23, whose face was covered with blood as he staggered away from the melée, said: "I was in the front line. People were trying to push forwards. I had my hand behind my back and was shouting at the officers that I was not trying to resist and one of them just decided to baton me. He gave me no warning. A few people around me were hurt.
"All the rises in tuition fees will do is perpetuate the divide between the rich and the poor," he added.
James Samuel, 17, a London sixth-former going to university next year, said: "I have seen a girl get trampled and people squeezed against the fences. I think violence by the protesters is OK if that's what it takes to get things done. It's about time the English showed their passion for issues. This is our last chance to show them that the vote is not OK."
Nigel David, 18, from Preston, Lancashire, said: "I feel there's a whole overtone about what the Tories are doing to this country: their idea of cutting things; removing key components of the welfare state; making it harder for people from underprivileged backgrounds to move up the ladder."
Police said that "extreme violence" against officers had led to peaceful protesters being refused permission to leave the square.
Protests around the country
Several hundred students and school pupils braved the snow to demonstrate in Glasgow city centre, winning a pledge from the Scottish Assembly that students would not have to pay the rises if they studied north of the border. Students and lecturers from a number of Scottish universities left an occupation at Glasgow University's Gilmorehill Theatre to trudge through the snow. A similar demonstration took place in Edinburgh.
Children as young as 11 marched alongside pensioners as up to 3,000 people took to the streets. The crowds were given a standing ovation as they marched past the civic offices in the city centre in what was described as a "carnival atmosphere". Many pupils had left school between lessons to join in the protest.
About 50 students took part in a noisy rally in the city centre, banging drums, singing, waving banners and shouting slogans against the planned fees rises. The students were mainly from Swansea Metropolitan University and the University of Swansea.
There was a largely good-natured demonstration involving nearly 200 people marching on Belfast City Hall. They began chanting as they approached the building.
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