The London riots began a year ago tomorrow. It is a sobering anniversary of an event that showed Britain, and particularly London, in the worst possible light. A year ago this seemed like a society in which anarchy lurked just under the normal order, where the disaffected young needed just an opportunity to ransack shops and businesses, and where the police were too fearful to control the streets. The social media, including BlackBerry Messenger, which were meant to represent the most liberal aspect of modern communications, were instead a means for rioters to connect with other rioters. The way we talked about the disorder reflected the shock we felt: back then, there was endless, self-scrutinising discussion about "Broken Britain", wanton criminality, and feral youth.

A year on, how different we look, how different things seem. The London Olympics, whatever else can be said about them, have shown Britain's sunnier side to the world. The thousands of hopeful, helpful volunteers who at times outnumber the visitors looking for directions are the other face of British youth. They have demonstrated that young people can be altruistic, community-minded, and kindly. As for the organisational triumph of the Olympics, it shows a London that is as different as possible from the out-of-control streets that we saw last year. The security operation, in which the army and police have made good the limitations of private operators, has been remarkable for its friendly efficiency. The forces of law and order are patently in control, as they seemed not to be a year ago. Where the riots presented an ugly and fractured aspect of Britain, the Games are an advertisement for the opposite. This is a time when society feels whole.

So, does this prove that last year's looting was a simple aberration and the real London is to be seen at the Olympics Park? Not quite. The riots did not present an untruthful version of Britain and the capital, but neither did they present a full one. The success of the Olympics gives a true version of Britain, but it is not the only one. We would be wrong to be wholly optimistic about Britain on the back of the Games as we would have been wrong to be unrelievedly gloomy a year ago. Policing in London has undeniably improved over the past year, as a result of the Met learning the lessons of the riots. But it takes no effort whatever to see signs of moral disorder: only last week, three teenagers were charged with stabbing a 16-year-old to death in south London. And the depressing aspect of the case was that it was by no means an isolated incident.

Are there lessons in all this? The obvious moral is that when individuals are united in a large common purpose, it can bring out the best in us. Even those who are critical of the Games on the basis of its enormous cost, and the narrow distribution of its benefits, have become rather patriotic about British successes. The legacy of the Olympics will include thousands of new homes in east London, with the Games already having rejuvenated one of the most deprived areas of Britain. The participation of so many people in a joint endeavour, from transport workers to spectators to volunteers, has made the Olympics seem like a project in which we all have a stake and not just in terms of our financial contribution.

This is, in fact, a wonderful period for Britain; a sporting festival which we will remember all our lives, and just the sort of thing that memories are made of. Let's enjoy the Games and relish the sense of celebration in the capital and the nation. Tomorrow's anniversary is significant, but it should not overshadow a great moment for the country. It's time to have fun.