In the end President Nixon resigned. Which, of course, provided a useful bookend for the film All the President's Men. One hesitates to state the obvious in a column purporting to offer insight, but without an ending there can be no movie. Which is why, according to Chris Bryant MP, there can't yet be any Hollywood treatment of the phone-hacking saga. It doesn't matter how many times the culture, media and sport select committee has met to discuss the same thing; we are not yet at the climax. Indeed, given how long it may take to conclude any hacking-related trials, we could be several years from the finale.

This is hardly ideal for James Murdoch or News Corp. The resignation of Rebekah Brooks has failed to draw a line under the scandal, because there is so much evidence to be trawled through, at 300m emails and counting. A company that tried so hard to contain the affair is now prepared to let the situation sprawl: witness the arrest of a Sun journalist, which has in turn helped fuel an atmosphere of fear and loathing at the tabloid once regarded as the most powerful on Fleet Street. As one veteran remarked: "Where did Rupert Murdoch think stories came from? Did they swim up the Thames to Wapping?"

If anything News Corp is trapped in a drama of the never-ending kind, a Dallas- or Dynasty-style soap opera, a tale of family disputes recounted in the pages of upscale New York magazines. The question, endlessly, is who will succeed Rupert Murdoch, and the issue won't go away because the 80-year-old shows no signs of moving on. Heir presumptive James has been wounded by the hacking scandal, but not fatally, and so inhabits an uneasy middle space. And so whatever News Corp actually does, the drama of succession, which is necessarily linked to the drama of hacking, hangs in the air.

Here, in medias res, starts the Leveson inquiry. He will report, in his first part, on the "culture, practices, and ethics of the press", the relationship between media and politicians and newspapers and police. Then he must make recommendations for a "more effective policy and regulatory regime" that supports integrity, freedom, plurality and several other positive notions. And all this is to be done before the phone-hacking story concludes in court or elsewhere, before we have an unambiguous sense of what happened at the News of the World. At the moment we are not even clear what occurred on 10 June 2008 when three men met to talk about Gordon Taylor.

Leveson has been given no small task, and there are many who want him to fail. Unpopular recommendations will undoubtedly be attacked, and while some editors may hope to lead Leveson towards a consensus of reform, there are enough people in the system, such as Richard Desmond, who won't go along with the prevailing view, particularly if Paul Dacre is involved. Reform, however, can't wait until the end of the script, because there is too strong a sense both on the street and in Westminster that in some areas the media is out of control. But it is not exactly clear what is proportionate: even newspaper groups are struggling with what is right. Witness the debate as to whether the use of private investigators should be banned.

In all this complexity, it is better to simplify. It is not worth hoping for the resignation of either Rupert or James Murdoch, even if that might solve the Hollywood problem. But it is worth aiming for one thing. We got here, in part, because one media group became too powerful. That cannot be allowed to happen again, which is why a minimum outcome of the Leveson inquiry would be reform of Britain's lax cross-media ownership laws. As the US constitution recognises, everyone needs to be kept in check.