Whether reporters should be prosecuted for crossing the line between legal and illegal conduct often turns on whether or not what they have exposed is in the public interest. One of the big problems in such cases is that "the public interest" has no legal definition.

In February, the Director of Public Prosecutions promised the Leveson Inquiry that he would address that issue. The guidelines he issued yesterday singularly fail to do that. The DPP, Kier Starmer, announced his intention to "give clear advice" to prosecutors and police "in these sensitive and difficult cases" – more than 40 people are currently on bail on allegations of phone hacking and other wrongdoing. We cannot duck the issue, he said. That is precisely what he has done; yet that may be for the best.

Asked at his press conference how past decisions might have been different under his new guidelines, he had to admit that the decision not to prosecute the Conservative politician, Damian Green, after claims that he leaked confidential information to journalists, would have remained the same. So would the decision not to prosecute a Sun journalist who used covert methods to expose cash bribes to a court clerk at Redbridge. So would decisions not to prosecute Telegraph journalists over the leaks on MPs' expenses. And on it went. Yesterday's guidelines, which are open for consultation until July, do not change the law but merely set out prosecutors' current approach.

Indeed, they set another hare running by suggesting that journalistic criminality might be outweighed by public interest considerations where the media are "raising or contributing to an important matter of public debate".

The old maxim about the public interest not being the same as what interests the public is just given new impetus. What we are left with is the continuance of the present system, whereby legal precedents are built on the careful weighing of each case on its individual merits.

That may be less neat, but it will probably make for better law.