Britain was once famous for its unarmed and relatively restrained police force, but the death of a man at last week's G20 protests in London has brought into focus serious concerns with a new aggressive form of policing. Former police chief Andy Hayman today warned that "If left unchecked, we have a more violent crowd in uniform than the one demonstrating."

Here I give my account of the protests and the police tactics used. This article was written several days prior to the release of the video showing Ian Tomlinson, the man who died at the protests, being beaten and pushed by a baton-wielding policeman shortly before his death.

Does Britain now have an aggressive system of policing that undermines the country's democratic traditions by systematically intimidating and closing down any protest it does not consider ‘safe'? The way that the G20 protests were managed suggests that we do. In particular the policy of "kettling" is a deliberate form of indiscriminate, collective punishment of demonstrators committed to peaceful protest, which seems designed to frighten people from expressing their disapproval of a system that is now, even by its own admission, dysfunctional. The development is part of a wider pattern of state authoritarianism not to speak of out-of-control policing. I was present in the City of London throughout Wednesday's events. Here I give my account of the protests, and an overview of the reports about them, with some ideas on how we can re-claim our liberty from those who would undermine it through fear and bullying.

Since Wednesday April 1st there have been several first-hand accounts by protestors of the heavy handidness and, in many cases, brutality of the police's approach to the protests at the Bank of England and Climate Camp. These have helped counter some of the all too predictable smears coming from sections of the mainstream media. There is now a strong case which says that not only did the police action raise serious civil liberties concerns; it was counter-productive, provoking violence and endangering the safety of peaceful protestors.

The day started well enough. At 11am my friend Andreas and I gathered at Moorgate station in the warm sunshine with around two hundred other protestors. Together we followed the "Red horse" (representing war) down to the Bank of England where we were joined by my friends Clare and Tony who were part of groups following the other three "horsemen of the apocalypse" - the Green horse against climate chaos, the Silver horse against financial crimes and the Black horse against land enclosures. People were angry, as you'd expect, but the atmosphere outside the Bank of England was generally peaceful and good spirited. There were cheers as the four horses were paraded on the steps of the bank and we heard impromptu speeches denouncing bankers and politicians from the recently suspended anarchist Professor Chris Knight and a woman in a rabbit costume.

As others have testified, the atmosphere really started to turn sour around one o'clock when the police strategy became clear. Under this strategy, known as "kettling", protestors are kept penned into an area by walls of armed policemen standing shoulder to shoulder. No one is allowed to enter or leave the area for an undesignated time period and protestors are left without food, water and (worst of all) toilet access. One officer informed Andreas, who was trying to leave the demonstration at 1pm to get to work, that the earliest he could expect to get out was 7pm. The officer said that as they were expecting a "breach of the peace" they would shut down the whole area and would only let people leave once they had recorded everyone's details (which will doubtless be stored on the police's illegal intelligence database along with thousands of other innocent activists).

There was no reasoning with the police, such as saying "Excuse me, I'd like to leave to go about my business before there is a breach of the peace". It was obvious to everyone there that this strategy has been decided by senior commanders and was going to be imposed no matter what happened (the experience of trying to reason with over-zealous riot police is well-described in an article by Peter Hitchens who was caught up in a "human sweeping machine" screaming "It's not debateable!" at him having stumbled into protests outside the Israeli embassy in January on his way home from work). As Sunny Hundal put it, the Police "predicted trouble and then created the conditions for it." All protestors were now being treated like criminals with the predictable result that many became frustrated and sympathetic to the actions of the minority who had come to cause trouble, offering cover for their activities through the sheer numbers pushing against police lines.

It was only after the kettling began that the police barrier by RBS was broken and the branch had its windows smashed and computers stolen by a few masked anarchists. The attack seemed at the time more like a stage-managed photo op than a spontaneous outburst of violence, something also observed by those who watched it on television, it was pure spectacle (it was noticeable that RBS's windows weren't boarded up like the others, despite being right next to the Bank of England). I couldn't help feeling that elements from all three groups present had willed the RBS moment to happen and were relieved when the branch's glass exterior was finally breached - the protestors angry at the banks, the media who got the images for the storyline they wanted, and the police who had been talking up the threat of violence for weeks and now had a justification for their enormous expenditures and intimidating behaviour.

Not long after the raid on RBS, a police line on Threadneedle street on the other side of the enclosure was successfully challenged by a surge of protestors. Andreas managed to escape before the police re-grouped to seal off the new shape of the protest with their own new enclosure, whilst Tony, Clare and I headed with the main group along to HSBC.

Over the next few hours a game of cat and mouse ensued with police and protestors moving from street to street. The police would divide up the crowds of protestors into ever smaller holding pens and when they were inevitably challenged by people frustrated by trying to get out they would push them with their shields and beat them with their truncheons. Every now and then without warning they would advance aggressively on the protestors who would scatter and then re-group to challenge the police lines anew.

I later heard the group outside HSBC described in the media as the "hard-core" element. I saw plenty of fellow protestors with bloody skulls and I even saw one young girl being carried away unconscious from the front line, yet I saw very few protestors strike back. There were a minority throwing cans and other objects but most were remarkably restrained given the provocation. Neither did I witness much violence directed against property. To great cheers, the anarchist flag was raised up the flag pole of an office block opposite HSBC but I saw no attempts to vandalise the building or the bank.

Around 4:30pm we managed to escape through a hole in a bush next to police lines before they had the chance to seal it off. We found our way to the nearest pub near Cannon Street station for a much-needed toilet break. After stopping for some food and drink we headed to down to check out Climate Camp outside the Carbon Exchange on Bishopsgate. Here the atmosphere was peaceful and relaxed with a festival-like vibe. Tents were set up in the road and cheerful protestors, mostly, like me, still under 25, were sat around holding workshops on climate change, meditating and listening to music. The camp was surrounded by police but they seemed much less tense than those by the Bank of England and they let us into the camp without any hassle.

We decided to spend the evening in the camp and headed to the shops in Spitafields in search of supplies. When we came back 45 minutes later the whole camp was under siege, the entrances blocked by riot vans and rows of police. Not only had they sealed off the perimeters of the camp, refusing to let anyone in or out, they were creating holding pens within the camp itself, dividing it up into ever-smaller sections.

I could see no other purpose to the siege other than to provoke and intimidate peaceful protestors. If the police wanted to clear the area it would have made sense for them not to let people in, but why would they refuse to let people out unless their aim was to stir up a reaction? From outside the camp looking in we could see young people, hands in the air to show they were non-violent, being pushed around and in some cases beaten by police. According to reports from inside the camp the officers carrying out the beatings were covering their ID badges so they couldn't be identified. As well as violence and intimidation, the protestors in the enclosures, including women, had to suffer the indignity of urinating in public. I challenged an officer as to why they were doing this when the camp had been entirely peaceful. All he could say was that an "offence" had taken place, refusing to say what.

After hanging out in the friendly squat on Earl Street, dubbed the "convergence centre", we returned to Bishopsgate around 10.30pm to see if the siege of the camp was still going on (I was later sorry to learn that the squat was raided the next day at noon by dozens of police officers in full riot gear and allegedly carrying tasers. All the occupants were apparently cuffed, searched and made to sit outside on the pavement for some time). As we made our way back to the camp several of our group were searched under section 44 of the Terrorism Act.

By this point the media had left and the police were clearing the streets, charging at protesters with shields and batons. One of our group, who hadn't been walking away fast enough for the police's liking, was screamed at and repeatedly beaten with a truncheon.

Most of the violence I saw was being committed by a small minority with the majority showing considerable restraint under intense provocation from the police. One amusing incident illustrates this. A young German anarchist tried to get the crowd of thirty fleeing protestors pumped up. He grabbed a litter bin declaring that that there needed to be a stand, and used his lighter to set fire to the contents which he then dramatically tipped ontothe road making a small firey barricade. He was immediately reproached by his fellow protestors. "You're ruining it for everyone" said a young couple, who immediately proceeded to stamp out the flames out with their feet. "Come on guys!" he shouted, "What are you doing? Let's burn this city down!" As his desperate provocation was extinguished by his fellow protestors he left in disgust, presumably to Strasbourg.

When the news broke that a 47 year old man, Ian Tomlinson, had died tragically in a police kettle, the media were quick to swallow the line fed to them by the Met that police medics had been pelted with bottles when trying to help (the Evening Standard made the inflammatory claim that they were "pelted with bricks" before having to withdraw it from their website). This conflicts with eye witness statements which say that the collapsed man was being given first aid by a protestor who was pushed away and told to get out by police who refused to speak to the ambulance the protestors had on the phone. All of the witnesses deny the allegation that missiles were thrown at the medics. The Observer has now reported that he was directly assaulted by the police. We need an independent public inquiry into the death of Ian Tomlinson to establish the circumstances of his death.

Serious questions also need to be asked about the practice of kettling itself. In my experience it is a form of collective punishment for participating in a lawful protest. Astonishingly, the practice itself was recently declared to be lawful by the Law Lords after it was challenged under the Human Rights Act, by a protestor and an innocent bystander who were caught in a police cordon for seven hours in bad weather and with no access to toilet facilities at the anti-capitalist protests on May 1st 2001. Lord Hope ruled that the police's use of containment in these circumstances, which amounts to a deprivation of liberty, is justified by the "interests of public safety. The case is now being taken to the European Court of Human Rights who it is hoped will overturn this dubious judgement and rule in favour of fundamental rights.

Writing on the Guardian's liberty central (which has provided excellent coverage of the protets), John O'Connor, a former commander at Scotland Yard, attempted to mount a defence of kettling. O'Connor didn't engage with the human rights objections at all, instead claiming that "massive overkill results in less injury and damage to property". Counter-terrorism powers and the use of kettling have no doubt made life "much easier" for police chiefs, as O'Connor, says, but then again so would banning protest all together. The police have developed a brutal method to contain peaceful protestors, discouraging ordinary people from exercising their democratic rights.

If we value democracy then we're going to have to challenge the culture of fear-mongering perpetuated by politicians and the police with the help of a compliant media. As George Monbiot said reacting to Wednesday's events on his blog, the police know that "By planting the idea in the public mind that the streets could erupt into catastrophic violence at any time, were it not for the thick blue line thrown around even the mildest protest, they establish the need for a heavy police presence", justifying their massive budget and the accretion of ever-more powers which erode our civil liberties. Police and government have connived in the demonization of protest.

As well as the organisational self-interest of the police there are other dynamics at play. A recent Joint Committee on Human Rights report into the 2008 Kingsnorth protests raised serious concerns about the police's use of terror and anti-social behaviour legislation, and in particular kettling, to bully and harass peaceful protestors. What was Jacqui Smith's reaction to this report and to the police tactics on Wednesday? Not a peep. As long as the public can be led to see any protests against government policies and those of the G20 as necessarily violent and disruptive, alternatives to the prevailing social and economic system are de-legitimised and the narrow spectrum of party politics in this country is validated.

What can those of us do, who are concerned by the threat posed to our civil liberties by police fear-mongering and the repressive measures that go with it? I think we should join forces in a playful and self-confident way, encouraging guerrilla action, like that of the Smile at the Spies Group who have produced posters satirising the recent advertising campaign by ACPO and the Met which raises the spectre of terrorism and encourages us all to snoop on each other. A good place to start might be to organise a large public protest against aggressive policing to assert our democratic self-confidence and show that we're not afraid. The police say that we face a "summer of rage". Who's up for a "summer of freedom"?