Here is one law the police may not have expected they would have to uphold: the law of unintended consequences. Politicians, on the other hand, ought to be better acquainted with the notion, and better prepared for it.
What could be objected to about the Coalition Government's scheme to put on the internet a map of every street in England and Wales, along with the statistics on how much anti-social crime, mugging, violence and burglary has taken place in the immediate vicinity? Quite a lot, actually.
The official line from ministers is that it will give "power to the people". The scheme will be a keystone in the architecture of "Big Society" accountability. The new website will make us feel safer because – information being power – we will all be able to monitor local crime trends and do something about it.
But how? The Government says it's "about fighting crime together". The intention is not that residents should erect roadblocks at the end of their streets vigilante-style; rather that we should all contact our local beat officer or attend a public meeting. In this way, we will "drive the priorities" of the elected police commissioners who will be the Government's next innovation.
Yet it is hard to see public meetings inspiring fear in the hearts of teenage hoodlums. And the Coalition's plan is likely to cause additional problems. Fear of crime could rise among the vulnerable or elderly; knowing the statistics for crime in the neighbourhood, without a proper understanding of the statistical context, might prove that a little knowledge can be a dangerous thing. It is a potential recipe for impotence and fear.
Areas could become stereotyped and stigmatised so that insurance premiums rise, house prices fall and pizza take-aways refuse to deliver or taxi drivers to pick up. The maps could also tell burglars where the crime hotspots – and police patrol cars – are to be found, allowing them to go about their breaking and entering undisturbed. The distortion of police priorities that will follow, at a time when forces' budgets are being cut, could make this gimmick positively harmful.