Leading article: This grubby scandal takes on a dark new significance

Before this week, those with a vested interest in downplaying the phone-hacking story felt able to argue that it was not a matter of great concern to the general public. A few celebrities and politicians who had their voicemails accessed by journalists, we were informed, was of little significance in the great scheme of things.

This was always a disingenuous argument. Illegal hacking does not become less serious simply because the victims happen to be in the public eye. But the allegation that an investigator, working on behalf of the News of the World, hacked into (and deleted) the voicemails of the missing Surrey schoolgirl Milly Dowler in 2002 – and also the private messages of the parents of the murdered Soham children, Holly Wells and Jessica Chapman, in the same year – blows this argument away entirely. This was not only a disgusting intrusion into the privacy of anxious private families; in the Dowler case it interfered with an urgent police investigation.

Even if it is true that the phone hacking investigation was once an arcane obsession of certain newspapers and politicians, that is emphatically not the case now. The fact that both the Prime Minister, David Cameron, and the Labour leader, Ed Miliband, felt the need to come out in condemnation of the alleged offence yesterday reflected the extent of the public significance this saga has now taken on.

The latest allegations throw the spotlight, once again, on the two organisations which have been at the centre of this grubby drama all along: Rupert Murdoch's News International group and the Metropolitan Police. The alleged hacking of the Dowler phones took place when Rebekah Brooks was editor of the News of the World. Ms Brooks has since been promoted by Rupert Murdoch to chief executive of News International. Andy Coulson resigned as editor of the same newspaper in 2007 when a journalist he employed was convicted of hacking Prince William's voice messages. It is therefore hard to see how Ms Brooks can remain in her present position, even if it is true that she was unaware of the hacking of the Dowler phones (as she claimed yesterday) when she was editor.

There must also be a response from the Metropolitan Police to this latest twist. The force apparently found evidence of the Dowler hack in the notes of the private investigator Glen Mulcaire, which were seized as far back as 2006. Why did it take so long to investigate whether the Dowler family might have been targeted? Why did representatives of the force repeatedly fail to investigate the hacking when the evidence was apparently under their noses?

The Metropolitan Police's Operation Weeting unit, established in January, is now said to be taking the phone hacking affair extremely seriously. But we are still plainly some distance from a conclusion to this business. There are rumours of even more shocking revelations of malfeasance and illegality to come. What the public needs is some reassurance that the Dowler case is as bad as it gets. And if there is worse to come, we need to know about it sooner rather than later. And those responsible for such violations must be forced to face the consequences in a swift manner. This disgraceful affair has already gone on for far too long.