It is both fascinating and worrying to discover that if you are an innocent person who wants your police DNA record removed from the national basis, you have much more chance if you live in Yorkshire than London, and none at all if you live in Nottinghamshire. In this key area for civil liberties, you are at the mercy of your local chief constable.

Until the policy was declared illegal by the European court of human rights, the government planned to keep the DNA of the innocent forever, making us all suspects for life. Ministers, having dragged their feet for months, have now offered a system where they will only keep the DNA for six years. This is still unacceptable, because it is unnecessary in crime-fighting terms. A system similar to the one in Scotland, in which the DNA of those arrested but not charged for the most serious crimes can only be kept for three years would work well and gain public acceptance. We need to adopt something much more like the Scottish model in the rest of the UK.

It is that issue of public acceptance that worries me most. Once the DPP had declared I had no case to answer, following my arrest for leaking embarrassing stories about Home Office failures, I demanded that my DNA record be destroyed. After a certain amount of huffing and puffing, the Metropolitan police announced that I was an "exceptional case" and agreed. I was immediately flooded by letters and emails from some of the other million people in the same position as me, wanting to know how they could be declared exceptional as well.

There is no good answer, because as far I can see the only exceptional thing about my case was the publicity it generated: there are hundreds of thousands of equally innocent people who don't want to be on a database but who have been told to lump it. These are the people who the authorities should be worried about, because they are angry and alienated.

Among those who contacted me were magistrates, former army officers, compliance officers for IT firms, solicitors and many other businesspeople. In other words the respectable backbone of any healthy society. The sort of people who never have any trouble with the police, and are instinctively willing to help police officers when needed. The ones who wrote to me are now extremely angry, and many of them make the point that they now regard the police with suspicion and fear. If this carries on, the police will find that their job is much more difficult than it ever has been, because they cannot rely on the co-operation of the respectable majority. That would be a disaster for policing in this country.

So when ministers or police chiefs seize on the odd case, always with emotional pulling power, which they claim would not have been solved without a big DNA database, they should consider the long-term implications of an intrusive DNA policy. An alienated population seldom provides the tip-offs the police need to catch criminals, or the evidence in court needed to convict. This has been a problem at times within some minority communities who regard the police as hostile. How much more difficult life would be for the police if this attitude became widespread.

A smaller, targeted DNA database would not only be a more effective tool in crime-fighting it would act as a sign that the creeping expansion of the surveillance state was being reversed. In this instance civil liberties and the real interests of the police point in the same direction. The only people who still need convincing are current Home Office ministers, and the senior ranks of the police.