One would not wish the serene back pages of Review to become the scene of an ugly legal battle between the bosses of News International and me, so I will not say that it is clear, from this book, that Rupert Murdoch is a liar. There is indeed another reading: that he is suffering from amnesia. How else to account for the exchange, reported here on pp 216-7, between Philip Davies MP and Murdoch Sr, when Davies asked him if he would have expected to be told if an editor on one of his papers had made a payoff of £1m to an individual?

"No," said Murdoch. "He might say 'We've got a great story exposing X or Y' or, more likely, he would say, 'Nothing special.' He might refer to the fact that however many extra pages were dedicated to the football that week."

"But he wouldn't tell you about a £1m pay-off?"

"No."

Well, I'm glad we have cleared that up. Still, earlier this year the House of Commons culture committee report on phone hacking at News International described Rupert Murdoch as "not a fit person to exercise the stewardship of a major international company". Or, you might think after reading more of his vague and feeble excuses in this book, a whelk stall.

Where to start? Perhaps with our own Nick Davies, a journalist memorably described by Stephen Glover in the Independent as "a misanthropic, apocalyptic sort of fellow  the sort of journalist who can find a scandal in a jar of tadpoles." The authors of Dial M for Murdoch reproduce this without further comment (although Watson and Hickman later call him "one of the great exemplars of good journalism"), but they need add none: Glover's comment was made after the first stirrings, in 2009, of the phone-hacking scandal, about which you may since have heard one or two things. The Times said the Guardian had been guilty of perpetrating "selective and misleading journalism", a wording that also appeared in the News of the World's denunciation the day after.

You may think that you have heard enough about this whole business, and I must admit to thinking it was more of a duty than a pleasure to pick up this book, but really, it is important. It is the one book you need to read on the subject. And it is still a live issue, as we watch Cameron happily renege on his word and instead say that he will not, after all, abide by the recommendations of the Leveson inquiry. We might, from sheer weight of data and epic length, have become overwhelmed by details and feel that all we need to know now is News International = bad. It is, though, more important than that; and only reading this book has made it quite so plain how low the company fell. I know that I am, by writing these words in the Guardian, preaching to the choir, but really, there is some eye-popping stuff here. (Although I hasten to add that the shady practices exposed here are probably not only confined to NI operations.) Even what you might have called the more trivial crimes  say, the hacking of Sienna Miller's voicemail  have their own poignancy. Your sympathy for her may be attenuated simply because she is famous, but who deserves to have their love affairs exposed so casually and callously? You could argue that it is the public's very appetite for this kind of stuff that has created the monster; but after reading this you might begin to realise that it is the monster of tabloid journalism that has created the appetite.

Watson and Hickman (the former is referred to, sometimes disconcertingly, in the third person, but then he's an MP and Hickman's an Independent journalist, so presumably the one who crafted the sentences) have produced an essential book: simply by keeping a close eye on events, they have given us an invaluable tool for assessing the state of the British popular press, and for working out how much weight to place on any statement made by Rupert or James Murdoch. Keep this by your bedside and refer to it from time to time, lest your outrage soften.