"German activists to take Bella Centre", blares the headline in the Danish papers. An old man in a bar tells me nervously -- when he hears that I'm with the conference -- that "the hooligans are coming, we're very worried". The fate of the world's environment may hang in the balance down the road at the Bella Centre, but broken windows and burnt-out cars are what prey on the mind of many Copenhagen residents.

It's driving most activists mad. Here they are, working their bums off to create striking, powerful, but non-violent uprisings that will stimulate debate or even political change, and all the journalists want to ask about or write about is: "When does the ruck start?" The piece in the Danish paper Politiken is typical: the "taking" of the Bella Centre turns out to refer to the well-publicised plan to try to hold a People's Summit in or near the conference next week, not a master plan for holding delegates hostage.

Why is this? Why this obsession with a small number of people throwing bricks? There are, I think, two reasons. First, thanks to the media and the police, the threat is often blown up far larger than the reality. Headlines such as the one above are unhelpful, but the police are also well aware that a few good scare stories do a great job of keeping people away from legitimate demonstrations, and make their job easier as a result.

We saw a classic example of this in the UK last year when the Observer published a story about the "growing threat from eco-terrorists", which the paper was later forced to withdraw: the piece was based almost entirely on information from the police force and little or no evidence from among activists had been gathered to back it up. Scare 'em off, think the police. Frighten them away and we'll have a nice, quiet afternoon.

But there is another reason for these stories. And that is that the threat from small groups of militant protesters is not just a police and media fiction. We may be guilty of hyping it up, but it is more than just a fairy tale; the Black Bloc does exist.

British activists tend to insist that it's all rubbish (to be fair, in the UK the Black Bloc really is a bit of a myth). But over here in Denmark, most Danish activists nod and say, "Oh yes, they're here already", or "They're coming from Germany". Every single local and police source I've spoken to since getting here has confirmed this. It's not just a little media fantasy. The next week and a half could get very nasty indeed.

So. If Vandal hoards really are pouring in for a ruck outside the conference centre, don't we deserve to know in advance? Don't I have a journalistic duty to report on them? Violence, rioting, these are profound disturbances of our social contract. Non-violent activists may want to tell us all about climate change, but the old man in the bar is just worried about a brick through his window. He deserves to know what's going on, too.

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