The river glideth at his own sweet will:

Dear God! the very houses seem asleep;

And all that mighty heart is lying still!

"Upon Westminster Bridge", William Wordsworth

One night in December 2010, underneath the Palace of Westminster, lit only by the lamps on the bridge and Big Ben in its yellow nightgown, I had a unique, protracted view of the scene that so captivated Wordsworth; its stillness, and its majesty.

I had little choice in the matter. Along with around 1,000 mostly young protesters I was imprisoned there, on Westminster Bridge, in sub-zero temperatures, for more than two hours. Some were not released for four hours – by which time it was almost 1am.

We were held in such a tight space by the Metropolitan Police that some protesters suffered respiratory problems, chest pains and the symptoms of severe crushing. With the walls on either side of Westminster Bridge barely waist-high, it is also miraculously lucky no one was squeezed out into the icy depths of the Thames below, where death would have been both inevitable and horrific. This is the tenor of modern protest in Britain.

Thursday 9 December began brightly, a day of cold but dazzling winter sunshine, the sun sitting almost at eye-level. Twelve hours prior to the chaos on Westminster Bridge, 40,000 protesters had embarked on a march against the tuition fees increase, the abolition of EMA [Education Maintenance Allowance], and the wider Tory shock doctrine of cuts and privatisation. It was the fourth demonstration of its size in a month, timed to coincide with the vote on tuition fees in the House of Commons – and the march soon alighted in Parliament Square. Around 4pm, as a blazing orange sunset descended on what was at this point an overwhelmingly peaceful crowd, the riot police lines closed in, blocking all the exits to the square, and the lid was put on the kettle.

"Kettling" is such a British verb; a darkly comic inversion of the national obsession with the serenity and salvation to be found in a "nice cup of tea" – and it has come to be the zeitgeist signifier of Britain's new age of protest. It describes the corralling of protesters in a confined space without food, water, or toilet facilities, for indeterminate amounts of time. It is de facto imprisonment without trial, and represents police brutality at its most strategic, artful, and devious.

And yet, and as much as it must be banned (a legal challenge is currently underway), I'm increasingly positive about what kettling has done to a generation of young protesters. Firstly, it makes them realise they have to make their voices heard outside the walled city – nothing is as poignant, or as enraging, as having your chants rebound off the police lines, forever echoing back and forth amongst the converted. Seeing the gap between the media narrative and the reality of the kettle is a head-mangling epiphany. The first time you get home from a demo where you've seen your friends truncheoned, to turn on the TV and hear kneejerk condemnations of "feral thugs, hell bent on violence" is as transformative an experience as the truncheoning itself. When I go on UK Uncut or student demos now, the young participants know to look out for kettle lines advancing, and they know they should be directing their chants and leaflets to shoppers, passers-by, and non-protesters. They are children of the information age, and kettling has brutally affirmed to them that a flash-mob or a demo that speaks only to itself is a missed opportunity.

Secondly, it's a timely epiphany for a whole generation, about the lengths the state will go to to protect the advances that have been made since 1980 in enriching the rich, and dismantling the public sector and the welfare state. It is often observed that kettling is designed to dissuade people from coming out to protest: if anything, it has the reverse effect on those who've experienced it. As protesters finally shuffled out of the Westminster Bridge kettle in single file, after seven hours imprisoned in freezing temperatures without food, water, toilets or freedom of movement, I saw several of them look the police in the eye and say, some with cheerful humour, some with snarling anger but all with total defiance, "See you at the next one, mate." The kettle is neoliberalism's most apt strategic deployment – and as a public order policing tactic, it is as risky as its philosophical underpinning. The intent is to suffocate protest with "containment", to stifle the swarming dissemination of dissent, territorialising with hard lines; but in fact it agitates and intensifies: it pushes the dilettante protester into becoming a hard-liner, a kind of abstracted agent provocateur.

There has been a psychic revolution since the glass shattered at Millbank in November – and the new reality has been a shock to everyone. In Parliament Square you could see teenagers testing the edges of the kettle and feeling its barbed-wire edges, like animals caged for the first time. Pinch me to see if I'm awake, they cry, and then run back, eyes bulging with adrenaline – I saw it after darkness fell that night, when conviviality turned to intense anger: that same full-body blood-rush of fear and excitement you get if you've been in any kind of physical confrontation. It affects you physiologically, your nerves bristle and tingle, and you can't help but come back for more.

Those kids on the front lines looked variously scared, angry, cold, laughing, fighting, hurting; but they were all there: awake, and alive – bashing into riot shields just to check it was real. It was. Walking into the main quad at University College London during the month-long winter occupation, I was confronted by one especially memorable slogan: "THIS IS ACTUALLY HAPPENING."

The smashing of the glass in Millbank tower in November marked the first assault on what Mark Fisher calls capitalist realism, the weary belief that "nothing can be done" about capitalism. Its physicality saw it dismissed as wanton vandalism, but it represented the much-needed re-emergence of young people into the public sphere. The months that followed saw a non-stop flurry of debates, public meetings, rallies, marches, occupations, and headline-grabbing viral actions against tax-avoiders by the likes of UK Uncut, NHS Direct Action, and the University for Strategic Optimism. Scores of university buildings have been occupied, as well as Conservative HQ, several town halls, government departments, schools, banks and shops. This energy lies latent for now, but the autumn term is just around the corner, and the cuts have barely bitten yet.

"THIS IS AN IDEOLOGY" said one placard I saw on the TUC-organised March for the Alternative in the spring. It was just those four words – the "ideology" in question is not a written bullet-point manifesto, not yet, and the danger is it will never become one: but for now, it's a vital affirmation of a world beyond Fukuyama's "end of history", and beyond capitalist realism – until it calcifies into a propositional political agenda, protest and dissent is the ideology of the kettled generation. "Don't call us post-ideological, like it's an insult, like we don't stand for anything" is the message emerging from a generation too young to even remember the Cold War.

Among the countless slogans that were chalked on the ground in Trafalgar Square on the day of the TUC demo, one stood out: "I MELT THE GLASS WITH MY FOREHEAD." It captures the psychic transformation Britain's young protesters have gone through: smashing through the glass at Millbank, struggling through the kettle lines, and finally piercing capitalist realism's façade: an aperture through which now flows the pent-up energy, imagination and passion of a generation who will need to use all three, extensively. I'm not going to pretend I knew where "I melt the glass with my forehead" came from – I looked it up later. It's a line from a 1915 work by the Russian utopian poet Vladimir Mayakovsky, called "A Cloud In Trousers". Those feral thugs are at it again, I thought.

We have a few years: the cuts may be deep, fast, and severe, but this is still, as the motto upon the storming of Millbank declaimed so vividly, just the beginning.