It warns that 'if you do not mention now something which you later use in your defence, the court may decide that your failure to mention it now strengthens the case against you.' In other words, a suspect probably still in a state of shock must there and then envisage the outlines of his defence, while knowing scarcely anything about the case against him.
Less attention has been devoted to the other project which the Home Secretary dusted off on Thursday, anxious no doubt to be back in the news after a quiet summer: his plan to set up a computerised national register of DNA profiles based on samples taken from those arrested for any recordable offence. Like the virtual abolition of the right to silence, this formed part of the Criminal Justice Bill. Unlike several other important provisions, it survived the severe mauling given to the Bill by Law Lords and others in the Upper House.
The fight against crime deserves a high place on the political agenda and an adequate share of available resources. Yet the enthusiasm with which Mr Howard has embraced the DNA profile data-base project is suspect. With its promise of near-miracle solutions to many crimes of violence and an increasing number of burglaries, its political attractions are evident. In reality, DNA profiles are considerably more fallible than once imagined; the likely cost of the plan is huge; and the potential invasion of privacy alarming.
Compared with DNA profiles, finger- printing is at the trailing edge of technology and therefore not politically sexy. No one questions its importance, but no Home Secretary has yet bothered to ensure that the national collection of fingerprints can be automatically scanned. The cost of running the proposed DNA profile network has been put at pounds 30m a year. That is based on 500,000 recordable crimes leading to DNA analysis, with each sample costing an officially estimated pounds 65- pounds 80 to process. Last year's budget for the entire forensic service was pounds 43m.
DNA profiling involves highlighting 'markers' that occur at a number of locations on a chromosome. Markers are a characteristic sequence of chemicals, repeated many times. Experts believe the chance of an innocent person's profile matching that of a sample taken at a scene of crime could be as high as one in two if the database contained 400,000 profiles. Contamination within laboratories is also possible. Several recent convictions based on DNA sampling have been sent back to the lower courts for retrial by the Court of Appeal. In short, DNA evidence alone is not enough.
The most worrying aspect of the enterprise is, however, the prospect of intimate personal information about heredity and susceptibility to disease being stored in official computers and therefore susceptible to leakage. That is why the operation must be not just properly funded but very tightly regulated. There should be well-defined criteria specifying from whom samples may be taken, to whom they will be available and for how long they can be held. All samples from those not convicted must be destroyed. The courts will also need to take a rigorous view of the evidential value of DNA material.
It is right that DNA profiles should take their place in the arsenal of weapons used by the state to combat crime. But there is a real danger that access to them might eventually come to be expected by insurers, banks, even employers or marriage partners. Even in its battle against crime, there are limits to the infringements of liberty that should be sanctioned. Indiscriminate telephone tapping is an obvious example. The consultation process initiated this week by Mr Howard will need to be robust and comprehensive.Reuse content