I'll trade a little liberty for a little less crime

Under current rules, such samples can only be taken from those stopped for a crime that could warrant a jail term. Nonetheless the police have already built up the world's largest DNA database, totalling 3.4 million samples, more than five per cent of the population. Well over a thousand more samples are added every day.

Civil liberties groups have long been warning about the threat this represents to freedom and privacy.

They say it blurs the distinction between those who have committed a crime and those who have not and they fear rather vaguely for the future. We can't predict who will one day use this database, they stress.

That's true, of course. But then nobody can say what will be technologically possible in the future in any case. What we do know is that the database already provides 3,500 matches a month last year, 422 matches against homicides, 645 against rapes, 1,974 against violent crimes, 9,000 against burglaries. That seems a worthwhile result. If it can be improved upon by extending the database, that too looks like a great idea to me.

No doubt because I am white, middle-class, and tediously law-abiding, I have never had any fear of the police or a significantly negative experience with them.

On the other hand, since moving to London, I have been burgled five or six times, twice extensively. I have had my car broken into rather more often. I have been a victim of protracted identity theft and credit card fraud.

Last Sunday, in a VirginActive gym, my locker was broken into, among others there that day, and my money stolen, no great tragedy, just enough to sour the day a little. In not one case was there even a suggestion that anybody might ever be pursued for these crimes.

It's nothing terrible, an average London life. But, like most people, I want to shorten the odds against criminals, even at the expense of possible inconvenience or intrusion on privacy for us all. And I find the police case that there's a possibility that those who commit minor offences might escalate to more serious crimes pretty plausible.

When I first lived in Dalston, I used to remonstrate with children who dropped their cans and packets straight from their hands on buses and at stops. I soon stopped that, which is probably one reason I'm still here. Then I tried saying nothing but quietly binned the trash myself.

That, too, got me violently threatened for showing disrespect. So that was a fairly fast escalation from a little light littering. The police need all the help they can get, I think..