It is tempting to blame all the demos and violence in the streets of London on the economic crisis. But I think that would be a misreading. The fact is that the British - and many other Europeans - have long enjoyed a good riot. The thing that needs explaining is why we haven’t had much social disorder since the turn of the century, not why it has returned now.

When I was growing up in London we had the Notting Hill riots in the 1970s, the Brixton riots in the early 1980s, riots in Liverpool, all the disorder linked to the miners’ strike, the Poll Tax riots at the end of the Thatcher era. If you want to go a lot further back, you could mention the Gordon Riots in 1780; the Chartist riots in the mid-nineteenth century.

And that’s just Britain. Obviously, the French have an even livelier tradition of social disorder and street riots. And just before 9/11, it began to look as if no meeting of European leaders would be complete without being set against a background of anarchist demonstrations. In July 2001, I went to an EU summit in Gothenburg where most of the city seemed to have been trashed by the “black blocs” of assorted European anarchists.

But, after 9/11, all this seemed to have stopped for a while. Maybe security was tightened up; maybe even the anarchists felt that protests against globalisation were no longer quite the thing. Whatever the reason, for several years things have gone quiet. Of course, there were big demonstrations against the Iraq war - but they had a coherence and a focus that the anti-capitalist demos lack.

So, while it is tempting to hail the street protests against the G-20 as signalling some sort of new political era of protest, I think it is the opposite. It’s back to business as usual.