The most damaging charge that can be made against political leaders at a time of national crisis is that they are unserious. The depiction of Boris Johnson as a jovial, careless rule breaker is precisely consistent with the image which has played to his advantage with the public until now. In other words, it rings true. That is the principal reason for the danger he is in.

The accusation that he was attending parties during lockdown was then compounded by the allegation that he lied about these events.

If that were to be proven it would suggest to most grown up minds that both his initial transgressions and then his need to save himself, allowed him to behave with irresponsible recklessness.

This suspicion might be confirmed by the barrage of briefing against his potential rivals for the leadership. In their eagerness to shore up support for him, his supporters are now pouring out streams of invective designed to discredit Rishi Sunak and Liz Truss.

Mr Sunak, who was widely believed to be more sound on low tax-small state economics than the prime minister who had apparently become a convert to democratic socialism, is now being presented as quite the opposite, as well as – God help us – soft on Brexit.

And Ms Truss who, until about twenty minutes ago, was known as the brilliant negotiator of fistfuls of global trade deals, is charged with failing to fly by commercial airline on one of her more arduous missions.

It is becoming pretty clear that this prime minister is serious about one thing at least – saving his own position – even if that involves undermining public confidence in two of his most able ministers. Suddenly this doesn’t look so jolly anymore.

But what does it matter, you might ask – especially if you are a cynical political sophisticate. Politics has always been a vicious game. Briefing against rivals is a familiar ritual especially when the stakes are very high. For that matter, there is now a good deal of evidence that the country is fed up with Partygate – who cares if he ate cake with friends and drank a glass or two? In the larger history of triumph over the virus, these are trivial matters.

But it is not the cake and Prosecco that is the great matter here – although it will never be forgotten by the people who, at the very same time, were not permitted to be in the room with their dying loved ones.

No, the real problem will prove to be whatever rash denials might turn out to be untrue, not just about the parties but the other thing that has surfaced – the airlifting of dogs and cats out of Afghanistan when there were people who might have had priority. Did he give his approval or not?

He has denounced the official communications which indicate that he did, as “total rhubarb”: a typically inventive Johnson locution which may or may not literally mean that something is categorically untrue. But like some previous examples of the genre (“inverted pyramid of piffle”) it also has that characteristic jocular tone for which he is renowned.

It is important to understand why flippancy and a casual attitude to ethical standards is such a very grave offence in public life. This has not always been the case. In some historical periods – Regency England comes to mind – the highest authorities in the land and those who enforced their will had a far less rigorous approach to righteousness.

Why do we now believe we have a right to expect national leaders not only to be paragons of personal integrity but to be dedicated to abstract moral principles like social fairness, or the advancement of aspiration, or the improvement of individual lives?

This expectation is now embedded so deeply in our conception of public life that it is difficult even to frame the question. We take for granted that all government policies need to be justified in terms of their contribution to the greater good – as defined by the central values of a coherent programme.

So when did we decide that politics itself had to be the practical application of a moral philosophy?

Of course, it is one of the fundamental assumptions of modern democracy that government should strive for the welfare of the many, so presumably the revolutions of the 18th century were an official beginning. But it can also be argued that it was the Protestant Reformation with its emphasis on the individual’s relationship to God and absolute responsibility for personal salvation that provided the foundation.

Certainly the idea that those who rule (or who administer) society have moral obligations, has always existed but I am referring to something more ideological: the notion of a body of principle and belief which must underpin every civic and economic proposal.

This is a relatively new thing. It is now taken for granted as legitimate grounds for criticism of a politician, especially a prospective leader, that he or she appears to lack commitment to a vision of what society should be like which can guide policy decisions.

The most potent critique of a sitting government is that it has no ultimate plan for the design of society, or else that it purports to have one but has betrayed it. Collectivism or free markets? Paternalism or individual liberty? State control or reliance on the community?

These larger, almost metaphysical, debates got properly under way in the nineteenth century when communism and capitalism began their epic battle over the fruits of the Industrial Revolution. They have provided the substance and the basic vocabulary of public discourse ever since. Since the end of the Cold War they have taken on, if anything, a more pervasive form.

Politics is still a life and death battle of ideas. The behaviour of Western electorates is incomprehensible without this understanding: politicians may be reprobates in private but their relationship with the country is a sacred trust.

You might be a lovable scoundrel but you still have to stand for something and mean it.