Leading article: Those who eavesdrop hear nothing good about themselves

It is now three years since a News of the World journalist, Clive Goodman, was jailed for hacking into the private mobile phone messages of Prince William.

But there are questions about this affair that have never been satisfactorily answered.

News International, the parent company of the News of the World, claimed at the time of the conviction that Mr Goodman was a single bad apple acting upon his own initiative; it was said that even his editor, Andy Coulson, did not know what he was up to (although Mr Coulson felt the need to resign in the wake of the scandal). And when Parliament's Culture, Media and Sport committee released a report earlier this year suggesting that the practice of phone hacking had, in fact, been widespread at the paper, News International issued a vehement denial.

But this week those denials came under extreme pressure. There have been fresh allegations that Mr Coulson not only knew about the phone hacking, but also that he actively encouraged the practice. The incendiary suggestion has also been made that the decision of the Metropolitan Police not to launch a wider investigation into phone tapping by the News of the World was influenced by the force's close relations with the newspaper – and that information was withheld from the Crown Prosecution Service for the same reason.

Some of the alleged targets of the phone hacking operations (including the former deputy prime minister, Lord Prescott) are now threatening legal action to get to the truth. The former culture secretary Tessa Jowell has revealed to this newspaper that she was told by the police that her phone had been hacked an astonishing 28 times. The Labour MP Tom Watson has written to the Government to request a judicial review of the Metropolitan Police's handling of the whole affair.

A judicial review seems appropriate. The impression that the police are too compromised by their relations with a single newspaper to investigate breaches of the law properly is simply too toxic to be allowed to stand. Public confidence can now be restored only by independent scrutiny.

This affair is also of profound political importance. After his resignation, Mr Coulson was hired by David Cameron as the Conservative leader's press spokesman. And he has been by Mr Cameron's side ever since. Mr Coulson is now director of communications at Downing Street, a publicly funded and powerful position.

Some regard Mr Coulson's behaviour in Downing Street as an improvement on the aggressive media management approach of the Labour years. He is said to be is working in a collegiate manner with the Liberal Democrat press team. That might be true. But if it turns out that Mr Coulson's role in the hacking scandal was different from what he has claimed in public, his present position in public life would surely become untenable.

And the fact that Mr Coulson was hired by Mr Cameron in the first place raises questions about the Prime Minister's judgement. At the time, Mr Cameron brushed aside warnings that Mr Coulson's record made him an inappropriate appointment, claiming "I believe in giving people a second chance". The more that emerges about this affair, the more dangerous Mr Cameron's insouciance appears.