Analysis: Delaying tactics saved PM today, but his future still lies in Coulson's hands

With one bound he was free? Not exactly. David Cameron gave a bravura performance in the Commons yesterday. There was no sign at all of sleep deprivation, although his late return from Africa on Tuesday and the need to brief himself will have meant he had little rest before going to the House.

Instead, the Prime Minister was relaxed, combative, dismissive and, at times, at his contemptuous best. He essayed his famous Commons humour, calling Ed Miliband leader of the "slumber party" in a laboured and unfunny reference to Sarah Brown's "sleepover" party at Chequers with Rebekah Brooks. Can someone please get a decent joke writer into No 10?

The Prime Minister showed once again that he is the coalition's greatest asset. Who else in government could have done this? No-one, with perhaps the exception of William Hague. But his strength in this regard highlights a weakness in the coalition. Labour had a phalanx of good Commons performers. Blair was pre-eminent. But think of Brown, Blunkett, Reid, Mandelson, Beckett, Clarke, Milburn and Mowlam. The coalition relies on the Prime Minister, and his currency is rapidly being devalued. The 14 policy reversals in the last year have probably finally eroded all opportunities for a honeymoon apology, mea culpa and policy reverse.

The underlying problem for the PM is not the detail of the News of the World hacking scandal. He shunted that off to a judicial inquiry. Nor is it the police investigation into hacking which on current staffing is estimated to be a ten-year job. One thing is certain - Mr Cameron will not be PM in 2021.

The problem is the stench around the NoW now symbolised by its hacking of the phone of the murdered schoolgirl Milly Dowler alongside the fact that until recently he employed a former editor of the NoW - Andy Coulson. The public understanding is simple, rough but not unfair - a guy who must have known about phone hacking was one of the PM's closest advisers. How can that be? Did Mr Cameron not know or not care? The rest is irrelevant. This is about judgment, and really about gut instinct. Nothing more, nothing less. Mr Cameron's problem is that the line of argument that Coulson was the editor, so he must have known because he will have checked the sources of the front page scoops, makes sense and is easy to answer. The PM's story is the complicated one. I had no proof. So, did you ask him outright? Did he lie? And there's no answer to those latter two questions.

On reflection, what stuck out at PMQs was the strategic silence on key questions. Had Neil Wallis, the former deputy editor of the NoW and the man whose employment had brought down two senior police officers, been in to see Coulson? The PM didn't have that information. The same tactic was used to deny the Commons the name of the firm which vetted Coulson. It will come out - it has to since public money was used. It just won't be in tomorrow's papers.But delay is not success. It simply defers the day of judgment and it links Mr Cameron's fate further and further to Coulson's. The flashpoint is likely to be over the issue of perjury - lying to the police, lying to court.

If proved this would spark a firestorm - and Cameron would not be exempt because some months previously he had been good in the House. One slip by Coulson, a major breakthrough by the Met, another New York Times investigation, pulling at the threads exposed in the DCMS select committee on Tuesday - each could be devastating. Mr Cameron's fate is now out of his hands.