Even by Scott Morrison’s standards, it has been an extraordinary performance.

His “I don’t hold an inquiry, mate” is making his “I don’t hold a hose, mate” look good.

On Wednesday the Prime Minister doubled down on his refusal to allow any sort of inquiry into what his Attorney-General did or did not do in 1988, closing off the opportunity for a credible investigation to clear Christian Porter’s name of an allegation that otherwise will not go away.

Mr Morrison’s reason – that an incomplete NSW police criminal inquiry into the matter had been closed – does not make sense, either politically or ethically.

Repeatedly and rather mindlessly repeating “rule of law” and “prima facie” doesn’t solve his or Mr Porter’s problems.

The absurdity of the Prime Minister’s claim that civilisation as we know it would come to an end if there was an inquiry was quickly exposed on Twitter.

The great and good and ordinary folk alike have trotted out example after example of how inquiries beyond police criminal investigations take place in the real world.

Coming on top of the issues raised by Brittany Higgins, Scott Morrison’s intransigence does the image of government no favours.

(And while Ms Higgins’ matter is different from that facing the Attorney-General, it is hard not to notice that Mr Morrison called for inquiry after inquiry after inquiry over those allegations until he came up with something that had credibility. No, another job for his Mr Gaetjens wouldn’t do.)

As Mr Morrison has said nothing about his 1988 inquiry ban that holds up to scrutiny, we’re left to wonder whether it’s the old choice between incompetence or a conspiracy – or politics.

The political rule book on inquiries was read on Yes, Minister four decades ago.

“A basic rule of government is never look into anything you don’t have to, and never set up an inquiry unless you know in advance what its findings will be.”

That makes more sense than mouthing “rule of law” and “prima facie”.