What have civil servants, policemen, heart surgeons and judges (among many others) got that cabinet ministers conspicuously lack? Answer: due process when things go wrong, the basic elements of fair treatment. You may not feel too sorry for Liam Fox as he stalks away into obscurity, but be clear that he had a raw deal – and be even clearer that it is David Cameron's fault.

Go back almost 20 years, to the moment that John Major, wandering through No 10's moral maze, first published Questions of Procedure for Ministers. At last we, on the outside, knew how ministers were supposed to behave, what standards to hold them by. We were even allowed to complain, and so call them to account. Brilliant! Except that there was a big fat hole at the top where ultimate authority was supposed to lie. What happened if you complained?

I found out when the then chief secretary to the Treasury, Jonathan Aitken, seemed to be playing fast and evasive over a trip to the Paris Ritz. Here was a fat dossier of correspondence between him and me that seemed to raise grave questions of procedure. Could someone – ah! a trusty cabinet secretary – please investigate? Sir Robin Butler had the Gus O'Donnell starring role in those days. He found nothing that troubled him: he just asked Jonathan to comment, and Aitken wrote him a draft push-off letter to send on to me. Case closed. Appeal to Major? No: Butler's null points were final.

What value had a code with nobody to enforce it, then? What use, especially if the supreme arbiter when things got nasty was also the PM of the day required to express "full confidence" in erring team players before examining anything? The rules, the expectations, the reassurances and the level of justice delivered were all jokes if they weren't pulled together, top to bottom. Helpfully, the committee on standards in public life (John Major's clean-up squad) agreed.

Exit Major, enter Blair, exit Mandelson (twice) plus rather too many other brothers in a bother. Yet still Downing Street stood on its dignity. If scandal broke in government, it was for the PM to decide what became of the offenders. Here was one power of office that couldn't be stripped away – but also one that made the entire system a laughing stock. And – miraculous moment after 15 wasted years! – Gordon Brown finally came to agree. He appointed the retiring parliamentary commissioner (into MPs' conduct) as his special adviser on ministerial misdemeanours. Sir Philip Mawer would probe, question and produce a full report. No more bodging and blustering.

And so to Fox. Mawer, admirably equipped and ready to serve, is standing by in the clash of the Werritty verities. But Fox doesn't call him. He, bizarrely, asks his own permanent secretary at defence to do the job, after which the buck passes up to O'Donnell – as though the Aitken years, the Blair decade, the Mandelson messes, had never happened. A besmirched Fox departs, fuming. The prime minister is congratulated for standing idly by a rightwing opponent. Mawer's phone never rings. And the shambles lives again.

Curiously, as Mawer's Westminster successor moves in to examine a complaint about Fox's use of MPs' expenses, we see what ought to have happened first time round: charges, and due diligence in establishing their truth. Think General Medical Councils, industrial tribunals – or even Johann Hari under Independent scrutiny. That's what we'd all want for ourselves: a proper hearing ruled by proper processes. Yet, nothing remembered and even less learned, Cameron bodges along. Forget standards in public life. Think shuffling the parcels of blame. He'll live to regret it: and so, I fear, will those who seek too frailly to serve him.