32 people have been arrested for a range of offences, including criminal damage and trespass when a demonstration against student fees became violent in London.
Britain's most senior police officer has called for a thorough investigation into the policing of today's protests, condemning the clashes as 'an embarrassment to London and to us'.
Met Police Commissioner Paul Stephenson said the force should have anticipated the level of violence 'better'.
The demonstration descended into violence after a group of protestors smashed their way into the headquarters of the Conservative Party.
A number of police officers were injured after they came under attack from youths, some wearing scarves to hide their faces, amid scenes of chaos.
Eight people have been taken to hospital with injuries after the violence flared at Millbank Tower, next to the River Thames in central London.
The demonstration, organised by the National Union of Students and the University and College Union, started peacefully, with up to 50,000 students, lecturers and supporters, marching from Whitehall past Downing Street and the parliament.
But around an hour after the protest started, violence flared at Millbank Tower, close to the Tate Britain art gallery where the march was due to end with a rally.
Hundreds of workers were evacuated from the building, which also houses other organisations, including government agencies, as windows were smashed and a fire was lit.
About 50 protestors got on to the roof, dropping a large metal fire extinguisher on to riot police.
Water fire extinguishers were also let off from the roof and eggs were thrown.
On the ground, sticks and other missiles were thrown at police from a crowd of at least 1,000 spilling out on to the normally busy road alongside the building.
Placards and banners were being burnt, to cheers from the crowd, while protestors inside the building used chairs as they smashed and kicked their way through more of the glass frontage, effectively opening up the whole atrium to the crowd.
A confetti of torn newspaper rained down on the hundreds of protestors gathered outside the Millbank atrium after students gained access to the upper floors of the building.
Water also poured down on them, seemingly from a broken sprinkler system above.
A red flare was let off as the atmosphere within the crowd became increasingly volatile.
The crowd responded to the heavy police presence with loud booing, screaming and chanting.
Students who had got inside the building's atrium tried to pull down the few remaining huge sheets of glass.
Others hurled stuffed pillows while the chants of 'Tory scum' increased in volume.
A Conservative Party spokesman said that all its staff were 'safe' but could not confirm whether or not they had been evacuated from the building.
NUS president Aaron Porter said a small minority of protesters had 'hijacked' the march, describing the violence as 'despicable'.
He said the violence was not part of the organisers' plans, blaming the trouble on a 'small minority' he believed had arranged it beforehand.
'We talked about the need to prevent anything like this and how important it was to act in a responsible way. Unfortunately a minority have undermined us.'
The protestors in the Tory HQ building and on the roof released a statement which said: 'We oppose all cuts and we stand in solidarity with public sector workers, and all poor, disabled, elderly and working people.
'We are occupying the roof in opposition to the marketisation of education pushed through by the coalition government, and the system they are pushing through of helping the rich and attacking the poor.
'We call for direct action to oppose these cuts. This is only the beginning of the resistance to the destruction of our education system and public services.'
A Scotland Yard spokesman confirmed that there was a 'controlled release' of protesters who had been contained at Millbank.
They were being photographed individually, with the images compared with CCTV footage in an attempt to identify those suspected of criminal activity. Anyone thought to have committed an offence was then arrested.
Charles Stewart-Smith, a spokesman for The Reuben Brothers, the owners of Millbank Tower, said it was too early to estimate the cost of damage inflicted on the building.
He added: 'The Conservative Party only occupies a small part of the building, but many people have been scared and had their days disrupted as a result of this.'
