There has been a close focus in the press on the main actors in the judicial inquiry that David Cameron announced into the phone-hacking scandal on 20 July. The abilities of Lord Justice Leveson (pictured) and the panel of experts who will advise him do of course matter. As Joshua Rozenberg notes elsewhere, the challenge is for Leveson to run his inquiry to the standard that Lady Justice Hallett ran the inquests into the 7/7 bombings. His ability to avoid the cost and time overruns of the Saville inquiry into the events of Bloody Sunday are crucial.

Leveson was the QC who successfully prosecuted serial killer Rose West, though he did less well prosecuting comedian Ken Dodd for tax evasion where, some may recall, George Carman QC defending, and Dodd himself, were better at remaining on the jury’s wavelength. Leveson will need to be tuned to several wavelengths as he conducts his inquiry, and in the findings he reaches.

The composition of the experts panel that will advise Leveson has also been picked over at length. Two journalists from the high-brow end of the trade, a former Financial Times chairman, a former chief constable, a former chair of Ofcom, and the director of campaigning group Liberty form a thoughtful lineup. Whether it is the ­intention or not, this lineup looks reassuring to broadsheet readers and liberals.

But if there is a lesson from both the Lord Butler and Lord Hutton inquiries, it is that the remit of an inquiry is even more important. In the case of Hutton’s inquiry into the death of Dr David Kelly, his conduct of inquiry proceedings came in for very little criticism. Instead, it was the mismatch between what proceedings seemed to promise – a broad, open look at the full context of events – and the relative narrowness of the matters the inquiry was willing to find on.

And the remit of Leveson’s inquiry should be of close interest because it is broad – by some readings, very broad indeed. Consider this line from Cameron’s 20 July statement to the Commons: ‘We have… made clear that the inquiry should look at not just the press but other media organisations – including broadcasters and social media – if there is any evidence that they have been involved in criminal activities.’

Other parts of Cameron’s statement also widen the focus of the inquiry. He added: ‘With allegations that the problem of the relationship between the press and the police goes wider than just the Met we have agreed that other relevant forces will now be within the scope of the inquiry.’ And the inquiry will: ‘Consider not just the relationship between the press, police and politicians, but their individual conduct too.’

In closing, Cameron said: ‘Finally… there is the question whether everyone – the media, the police, politicians – is taking responsibility in an appropriate manner.’

To a degree the statement is the prime minister’s wishlist in code. And to avoid the judicial inquiry being used to serve Cameron’s aims, Leveson and his independent experts need to decode that wishlist. How they manage the inquiry’s sheer breadth will determine whether they ­succeed.

The events that have taken some incidents of phone hacking to the status of a ‘scandal’ involved a limited number of players: one newspaper; one company; one private investigator; one political party; and one police force. Hence, from events so far, the Labour leader Ed Miliband, the Guardian, the New York Times and the BBC are in the ascendant, as Cameron and Murdoch’s stars wane.

The broad remit of the judicial inquiry is intended to suddenly change the terrain. This is a gamble for the prime minister. It may or may not work. Viewed in political terms, one thinks of John Major, some way behind Tony Blair in the polls in 1997, announcing the date of the election long in advance of when he had to. The longer campaign should have been less predictable – a possible game changer, ultimately unsuccessful.

So the remit presents a bigger field for Cameron. At present, he is taking ‘responsibility’; he would rather it were ‘everyone’. Equally, taking the blame currently is a section of the tabloid print media, so broadcast and social media have been put in the frame too. The Metropolitan police is taking the heat at the moment – enter to the inquiry’s scope other police forces. Although he has consulted on the matter, its design – its remit – is very much set by the prime minister. Have Leveson and his experts therefore accepted a poisoned chalice?

Not necessarily. But they will need to guard against certain problems inherent in the remit Cameron has set out, to produce a report that commands public respect, and meets wider expectations of fairness.

This means that the inquiry must approach its review of broadcast and broadsheet media, of the police, of the role of law firms, and of politicians’ conduct in a way that is evidence- and intelligence-led.

The inquiry must find ways to quickly establish if any one of the parties whose conduct did not prompt this scandal – but who are now within the inquiry’s remit – merit close scrutiny. That may not be an easy task. As John Yates has discovered, dismissing a line of enquiry too quickly can be a poor decision.

But the inquiry must try on this count in order to retain its own credibility. If equal time is spent looking at a broadcaster where bribing and hacking were not ‘rife’ as at news outlets where these practices were, for example, then the inquiry will be open to charges that it has been used to political ends.

That would be a sad outcome for experts and a judge who at present all seem to be highly credible choices.