Leading article: Saying sorry is not enough. Only a full inquiry will suffice

It is unprecedented for a newspaper to publish as abject an admission of wrongdoing as the News of the World did yesterday, apologising "publicly and unreservedly" for having breached the privacy of an unnamed "number of individuals" and expressing its willingness to compensate the victims.

No one should be fooled by the News of the World's bathetic pose or effusion of crocodile tears. News International's "mea culpa" may sound contrite but it is nothing more than an attempt to draw a line under a story that won't go away. What the company executives have done is not nearly enough, and the limited nature of their admissions raises more questions than it does answers.

Peel away the lachrymose wording of the newspaper's apology and one soon comes across the bare bones of the same containment strategy that the company has pursued ever since the phone hacking scandal came to light in 2007. This is that the offences were the work and sole responsibility of a "rogue reporter" – since expanded to several, operating on their own initiative during a limited time, from 2004 to 2006, a period that coincided with the editorship of Andy Coulson, who resigned as David Cameron's director of communications in January. James Murdoch, the number three at News International's parent, News Corporation, admitted as such recently, telling a US broadcaster with evident satisfaction that the company had "really put this problem into a box".

This is manifestly not the case. The box keeps bursting open. Last week saw the arrests of the News of the World's chief reporter and its former head of news, Neville Thurlbeck and Ian Edmondson. Meanwhile, public figures keep coming forward with fresh allegations that the newspaper bugged their private conversations. As they do so, claims that these offences all took place within the period 2004 to 2006 appear questionable. The Independent on Sunday reported yesterday that the Duke of York believes the newspaper bugged princesses Beatrice and Eugenie only two years ago. George Galloway, the former independent MP, claims the newspaper hacked his phone back in 2003.

As the scandal continues to unfold amid a welter of fresh claims and revelations, News International's bottom line, which is that the illegal hacking of phones formed no part of the newspaper's "culture", looks increasingly threadbare. This, in turn, is bound to add to the pressure on the Metropolitan Police to explain why they were so dilatory in pursuing the case to start with. It may also have a knock-on effect on the deliberations over the future ownership of BSkyB, which News Corporation hopes to acquire. After the brief for handling this takeover was taken from the Business Secretary, Vince Cable, and handed to the Culture, Media and Sport Secretary, Jeremy Hunt, News Corporation received a green light to take full control of BSkyB in March. Last week, Mr Hunt's department was maintaining that the phone hacking scandal at the News of the World had no connection with the question of media plurality – the heart of the matter at BSkyB. This may start to sound hollow if it becomes clear that wrongdoing in the newspaper was much more widespread than the company admits.

As the lines of its defence crumble, News International is falling back on claims that calls for a more thorough investigation into its workings are a witch hunt by an establishment bent on keeping the Third Estate out of its affairs. But no newspaper has the right to break the law in a calculated and systematic fashion in pursuit of juicy stories. The cause of investigative journalism is not served by underhand, illegal, conduct, and when Labour leader Ed Miliband says we need to "get to the bottom" of what was going on at the News at the World, he is right to do so.