When the defence relies on alibi evidence the police have to investigate it before trial, and because of this it is rarely used successfully. In the United States Timothy Durham was accused of raping a child, even though 11 witnesses said that at the time he was in Dallas, 300 miles away. DNA evidence later cleared him of guilt, but not before he had served five years in jail. The prosecutor had said that 11 witnesses must be wrong, purposely or unintentionally, since the science, later described by Durham’s lawyer as junk science, could not be wrong.

In Britain Mark Dallagher, who had the unenviable distinction of being the first person to be convicted of murder based on ear print evidence, spent several years in prison before he was cleared and released in January. He had always asserted an alibi.

Whereas the innocent sometimes suffer great wrong, things are looking up for the guilty. The provisions in the Regulation of Investigatory Powers Act 2000 relating to the retention and use of intercepted material (such as mail or telephone calls) create a scheme that represents a real gift for the serious and organised criminal, or worse, the terrorist. Material retained after the use of a telephone intercept must now be looked at by the lawyer handling any prosecution, who must decide whether it undermines the prosecution case or assists the defence. If he or she decides that it does, it must be disclosed to the defence. However, the Act prohibits any disclosure that tends to suggest that the individual was the subject of an intercept warrant.

Consider then the case of the organised criminal who has reason to believe (correctly) that his telephone is being tapped. He is going to murder a criminal associate who has been informing the police. While committing the murder, he arranges for another associate to telephone his home, where his wife answers and lies that her husband is in the bath and will call him back later. The murderer arrives home shortly afterwards and phones his associate, apologising for being unavailable earlier. When he is prosecuted for the murder (the case against him is compelling) he claims that he was in the bath at the material time — both his wife and associate can verify this alibi. The prosecutor reviews the material, applies the “undermines or assists” test and concludes that the interceptions need to be disclosed. He cannot do so, however, since this would breach the prohibition.

There are few ways to get past the effect of the prohibition and on the facts set out above it would be quite impossible to do so. The only course is for the proceedings to be discontinued. There is an argument that suggests that the material should not be retained at all but this is almost equally unpalatable. Consider the possibility that an intercept did demonstrate an individual’s innocence; would the State have a clear conscience that it has destroyed potentially exculpatory evidence relating to a person that it seeks to prosecute?

The problems caused by the prohibition are acute and serious, as the Prime Minister’s recent review has identified. However, the proposal to introduce admissible intercepts may still not cure them. The exploitation of the provisions by serious criminals is only one of a number of problems with a piece of legislation referred to recently by the Court of Appeal as “a particularly puzzling statute”. Amendment is becoming an increasing imperative before the law becomes for the criminal and terrorist what Shakespeare described as “their perch and not their terror”.