Of the people who came for trouble, some are self-styled anarchists who have clearly done this before, but others seem to be trying on the garb for the first time - and it's not hard to imagine the thrill of hiding behind that face scarf. They are joined by a nice cross-section of London's everyday thugs: some football hooligan types, some street kids with their flat-peaked caps. It's still a very small minority, but for the next few hours there will be some trouble whenever enough of them gather at the same point on the police line. Of course, what makes this possible is the fact that almost everyone is gathered somewhere at the police line - that's where the action is - and any big concentration attracts curiosity and grows exponentially. Now there are taunts and plastic bottles thrown from the back, jostling at the front and a young man turns to take a grinning picture of himself in front of the riot police. Then a small surge, a few police batons rise and fall, and the crowd retreats. A moment later, a cheer: a dingy anarchist's flag - it's been lying in someone's reeking bedroom for months, waiting for this moment - has been run up the flagpole outside the Temple Court building on Queen Victoria Street.

The most serious violence that I witness occurs when the anarchists get their hands on some of the metal gate barriers that have been regrettably left inside the cordon. It takes only one or two guys to move one of these barriers and so only a handful of people are
responsible for fortifying the frontline of an essentially inert crowd against the riot gear of the police. For half an hour or so, a medieval battle is acted out, with the anarchists moving the barriers around to use them as battering-rams at different points on the police line, while bottles, some glass now, rain in from the back. This provokes baton charges from the police, who sweep forward, dealing painful blows to everyone in their path. I cower in a doorway during one of these and am left stranded behind police lines, where a tiny WPC pounces on some floored protestors one by one, swearing and savaging them with her baton.

At one point, the anarchists move the barriers 20 yards back to invite a charge. Amazingly, everyone acquiesces to this. The non-violent protestors move, like bewildered zombies, back behind the barriers, leaving a no-man's land that is immediately filled by press photographers getting their money-shots. It looks like a staged
photo-op or a film set and when the photographers withdraw, the police dutifully rush forward to fill the gap, and more people are hurt. Eventually, all the metal barriers are confiscated, the protesters get bored and, after a soothing interlude in which a mannequin dressed as a banker is set on fire, a new dance begins: for the last couple of hours at least 100 people rave madly to drum and bass music. Others are sitting around ranting about false imprisonment and a tall, straggly-haired youth emerges from the dancing throng and exhorts them to join him. No one listens, so he returns immediately, springing up and down on the spot, hands in the air, his fingers tracing vague, mystical runes against the night sky that are as meaningful and as necessary as anything I have seen today.