Face it: the anarchist kids in hoodies did the summit a huge favour

As I write this, I am looking at a picture of two crusties smashing a bank's windows, outnumbered about 25 to one by a solid wall of the nation's media. For any ordinary, decent anarchist, trying their best to do an honest day's vandalism, it's not just the police lines you have to get through - it's the pavement-to-pavement cordons of newspeople.

The rioters may have brought their own tank (or, more properly, armoured vehicle) but this is no Tiananmen Square. The TV pictures of aggro in the streets, like all TV pictures, are true as far as they go. But they focus narrowly on what is most dramatic, and largely exclude the reality that, even within the main demonstration area, there's a lot more aimless standing around and taking pictures on your mobile than there is bringing down capitalism.

The issues the G20 is intended to address are, of course, very far from boring. This year, of all years, was surely the one when we might have seen manifested the public's real disgust with our ex-Masters of the Universe and the insane risks they took with our companies, pensions and lives. Imagine the impact that a disciplined, dignified demonstration of hundreds of thousands - perhaps led by bodies that actually represent people, such as trade unions and churches - could have had.

Instead, we got 5,000 students in hoodies. We got "themed processions" by the "Four Horsemen of the Apocalypse", one of which, the Black Horseman, was described by the organisers as a protest "against land enclosures and borders in honour of the 360th full circle anniversary of the Diggers". Of course!

I was excited to see that the "G20 Meltdown" website contained a manifesto - until I actually read it. The G20 Meltdown manifesto contains precisely 69 words. You can almost hear them thinking: "Oh dear, we really do need to stand for something, don't we?" So up they come with this sloganising afterthought.

The more I watched the non-event in the City, the more I realised that it was the precise counterpart to the non-event of the summit itself: sound and fury, signifying nothing. There will not, as once trumpeted, be any major "new deal" at today's world leader meeting to stimulate the global economy. No country wants the G20 writing its national budget for them. Instead, the agreement is expected largely to reiterate the stimulus packages each individual nation has already announced.

There will not be a walkout over reforms to global regulation. Although journalists are doing their best to make this issue interesting, with "light-touch" Britain and America supposed to be battling Germany and France, no country seriously disputes that there is a need for greater controls. But though there may well be fierce declarations on the subjects of banker bonuses and tax havens, it is hard to imagine how a new global regulatory regime on these subjects could in practice work.

Despite the wider promises to co-ordinate, a global response to the crisis has often been lacking. British ministers are putting pressure on their newly nationalised Royal Bank of Scotland to favour domestic lending - quite understandable politically, but not at all in the spirit of working on what is best for the world as a while. Ireland's government unilaterally guaranteed all bank deposits without even telling the EU first.

Restructuring the world financial system is the fundamental challenge. But it is, as even Mr Brown's spokesman was forced to concede, a "process, not an event". Arguably, the key problem is rebalancing trade: convincing the big exporting nations - Germany, China, and Japan - to reduce their trade surpluses so the consuming nations - Britain and America - can reduce their horrendous deficits, something that would be in the interests of all. But that's not really on the agenda today.

This is a gathering of 20 sovereign states. Expect, perhaps, some "surprises" in the agreement that allow the leaders to claim a breakthrough. But what actually happens in all cases will depend on each of those countries - not just in the promises they sign up to, but how far they actually keep them. The even-more-overhyped G8 summit at Gleneagles in 2005 made some big commitments, but few were fully followed through.

Apart, perhaps, from containing some important (though still uncertain) changes to the remit and financing of the International Monetary Fund, the final summit communiqué today is likely to be essentially rhetorical, the rough equivalent of the G20 Meltdown manifesto in slightly prettier words.

The world leaders' presence will be largely decorative; most of the deal has been hammered out by anonymous officials in meetings over the past several weeks. The atmospherics? Yes, it's good that Barack seems to like Gordon - but will anyone remember it in a month's time?

For weeks, everyone involved in the G20 has been hysterically bigging it up. Gordon Brown hopes, or at least hoped, that it would rescue his premiership. The demonstrators have been feeding the media with thrilling predictions of mass chaos in the streets, hoping (alas, it seems, largely in vain) to provoke a police overreaction that would give them the moral high ground. Newspapers have been only too pleased to co-operate - it makes a great story.

But just as the anarchists in the City needed reporters and photographers to give substance to what turned out to be a relatively minor protest, the great circus of the summit itself relies on the media to confer on it an importance it does not fully deserve. And above all the suits and the anarchist crusties, those two great vessels each equally empty of inspiration, need each other.

The kids in Threadneedle Street yesterday may not like this, but they did the summit a big favour, simply by behaving as if it really mattered. It may, however, now be time for the rest of us to tiptoe away and leave them all to it.