The Leveson Inquiry is about to get even more interesting. Tonight, Australian time, the former News of the World editor Andy Coulson will be grilled in public for the first time since his arrest in July 2011 on suspicion of phone hacking and corruption.

Then on Friday, his predecessor as editor, and Rupert Murdoch protégé, Rebekah Brooks, will follow him into the dock.

Both are likely to put Prime Minister David Cameron under yet more pressure, because Coulson left the NotW in January 2007 to become the Tory leader’s head of communications, and ended up running the media operation at 10 Downing Street. It’s clear that he already knew a great deal about the extent of phone hacking when he left, even if he hadn’t sanctioned it himself (which seems unlikely).

Meanwhile, Rebekah Brooks, who has been arrested on suspicion of phone-hacking, corruption and perverting the course of justice, is said to be ready to tell Lord Leveson all about the text messages she and Britain’s PM sent each other, sometimes up to a dozen times a day.

Some reports suggest she and the PM both signed off with an “x” and that David Cameron sent her messages of support last July when the hacking scandal exploded, and before she was forced to resign as CEO of News International.  Then, of course, there will be all those texts about Rebekah’s ex-police hack (sorry, horse) that Cameron is said to have ridden.

Ah, there’s so much to ask. But some of the best questions will almost certainly be off limits, for fear of prejudicing Brooks and Coulson’s future criminal trials — should charges be laid. For example, we suspect Lord Leveson’s counsel Robert Jay QC will be unable to ask about a hugely damning internal email from September 2006, which detailed what police had supposedly told Brooks about the hacking investigation. The email was sent to Coulson, then the NotW‘s editor, by the paper’s top lawyer, Tom Crone, who has been accused by the House of Commons of being involved in a cover-up of the phone hacking scandal. Among its many revelations were:

  1. Police had informed Rebekah Brooks that there were hundreds of victims of hacking by the NotW‘s pet private investigator Glenn Mulcaire.
  2. Police had Mulcaire’s “recordings and notes” which demonstrated a “pattern of victims … one replaced by the next one who becomes flavour of the week/month”
  3. Police wanted criminal charges to “demonstrate the scale of GM’s [Mulcaire’s] activities … so they would feature victims from different areas of public life, politics, showbiz, etc”.
  4. Police knew Mulcaire had been paid around £1 million by the NotW for his work.

Despite knowing all this in late 2006, Coulson and Brooks continued to maintain on many occasions up to late 2010 — in public statements before the House of Commons and other places — that they were absolutely sure hacking was confined to one rogue reporter. This, of course, was utter tripe, as they very well knew.

So far, neither Lord Leveson nor the House of Commons has been able to confront Brooks and Coulson with the revelations in this email — which strongly suggests they misled the British parliament and the public — because it was only supplied to Leveson at the end of February 2012.

It will be interesting to see whether Robert Jay QC feels he can get into it at all and whether Coulson or Brooks will plead privilege against self-incrimination if he does.

But whatever happens, we are likely to learn yet more gory details of the way in which successive governments and prime ministers — Blair, Brown and Cameron — sleazed up to Murdoch’s powerful tabloid, The Sun, and to Brooks (its editor from 2003 to 2009) in particular.

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