When I set out to report on last week's London protest against fee rises and funding cuts, I didn't expect to find myself trapped on Westminster Bridge at 11pm in a crowd of 2,000 people pressed against a line of riot police.

Being "kettled" is a boring, frustrating experience at best. After some six hours of detention, desperation to leave took hold of the students, the vast majority of them peaceful. They raised their hands and chanted: "This is not a riot." The crowd pushed forward. The police line was briefly broken and forced back before regaining its position.

It was a troubling end to a day I began at King's College London, where a handful of staff from the University and College Union branch were among a contingent of around 300 that gathered outside the Strand campus.

As other groups joined up en route to Trafalgar Square, Jim Wolfreys, King's UCU president, talked about the 10 November march.

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"I've never seen anything like it in Britain before," said Mr Wolfreys, a lecturer in French politics who has written about protests on the other side of the Channel.

He saw a gulf between highly organised, union-driven protests in France and those in the UK.

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Last week's main march - attended by an estimated 20,000 - was organised by new student groups such as the National Campaign Against Fees and Cuts and the Education Activist Network. It had no official backing from the UCU or National Union of Students.

Tahera Aziz, membership secretary for London South Bank University's UCU branch, said there was widespread concern at higher fees among students at the university, which prides itself on widening participation. Students had been an "inspiration" to staff, Dr Aziz added.

The march route agreed between organisers and police would have seen demonstrators pass along the north side of Parliament Square and up Whitehall. But that did not happen. Some reports have suggested police blocked Whitehall, while police blame protesters for deviating from the planned route.

In Parliament Square, a small group of men used a metal placard as a battering ram against a police line as smoke bombs went off. Others pushed over metal fences and gathered in the grassed centre of the square. The police made no attempt to stop them, but at all corners of the square, officers in riot gear quickly moved into cordons. The kettle was first imposed at 3.30pm, I learned later, then intermittently lifted before becoming permanent at around 5pm (I eventually got out at 11.20pm).

There was no communication from the police that containment was starting, nor any warning to leave.

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In the evening, I tried several times to leave the square, telling officers that I was a journalist, but was refused. Most students milled around bored and cold, making it easy to spot the main instigators of violence - the handful of masked youths smashing blocks of concrete into chuckable chunks of rubble.

At one of the cordons, a crowd thrust metal fences (which, puzzlingly, had not been removed from the square beforehand) at officers, who responded with batons.

One man spent about half an hour trying to smash a bomb-proof window at the Treasury. A group of about 15 riot police eventually left their cordon to defend the building, before finding themselves surrounded by protesters and charging at them to scatter the crowd.

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Another group of protesters managed to open a door to the Treasury and shoved metal railings against the police officers defending from within, as helicopter searchlights flickered over the building.

Eventually, outside Westminster Abbey, the police started letting people out one by one. I spent an hour in a scrum of hundreds of people waiting to leave, packed in between the police line and metal railings.

All people leaving at this point were videotaped - the source for some of the Met's close-up images of suspects.

As I neared the front, the police announced that the dispersal was being shut off and everyone would have to leave via Westminster Bridge, where a new kettle was set up.

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Still trapped in the kettle two hours later, a female King's student asked why people wanting to protest peacefully outside Parliament had been detained, when "education is so important".

john.morgan@tsleducation.com.