Yesterday the Metropolitan Police put out a very short statement. They asked for “minimal reference” in Sue Gray’s forthcoming report on alleged parties in Downing Street to matters that the police are themselves investigating. Otherwise, there was a danger, the Met explained, of “prejudice to our investigation”.

Here, in miniature, is an illustration of one of the great problems of running a country nowadays. When people get excited about a political scandal, they reach for the criminal law. That is understandable, because they perceive injustice but, more often than not, it is unwise. Law and politics are quite different things. Mix the two, and worse trouble usually ensues.

Politicians themselves often invoke legality in this way, often for base motives. “Lock her up!” shouted Donald Trump as he campaigned against Hillary Clinton. After he gained office, he got a taste of his own poison when attempts were made to impeach him. When he left office, legal opponents came after him over the riot in the Capitol.

Here in Britain, people who hated Tony Blair because of the invasion of Iraq wanted him tried as a war criminal. During the later cash for honours scandal, he was questioned by the police.

One of the features of such cases is that, though they create much excitement, they rarely succeed. The complication of the story, the unreliability or scarcity of evidence, media over-excitement and the heat of political battle make it hard for a conclusion to be reached. The point made by the Met yesterday about investigations being prejudiced by other reports usually comes up. The thing tends to dribble away. Lawyers get plenty of money out of it, but that does not mean that the rule of law is well served.

Sensible police officers usually hate such cases. They know that, whatever they do, they will be accused of persecuting the politicians involved or of treating them too gingerly or – for public opinion is usually divided – both. They much prefer to deal with what Ulster police, referring to non-terrorist offences, used to call “ordinary decent crime”.

It is even quite common for police interventions to impede lesser forms of investigation, as seems to be happening now with the Gray report. If something is sub judice, little can be said about it.

Those gleefully chasing Boris Johnson over lockdown parties may now find their hunt stymied by delays and restrictions while detectives search ancient fragments of birthday cake for fingerprints (I exaggerate, obviously, but not much).

There is also a problem of disproportion and the misallocation of police resources. Many regard it as morally very serious if Boris Johnson and staff in 10 Downing Street broke Covid rules. But in terms of the criminal law, the offence is trivial, as is indicated by the penalty – fixed fines of £100. Is Plod’s journey to Downing Street really necessary?

Behind these problems lies a deeper question. Would it in fact be a good thing if the police, or other legal authorities, could bring down the leader of a democratic country?

We can all think of extreme examples where the answer would be “Yes”. If Boris Johnson, enraged by the sight of a former adviser’s beanie hat and his productions on Substack, personally stabbed the man, he should be arrested, tried and convicted, no matter how much he might complain of provocation. He would have to leave his job.

Even a less personal act, a wider governmental decision like, say, trying to beset BBC Broadcasting House with soldiers of the Household Division, should be prevented by the forces of law, however much one might secretly long for it to happen.

It is true, in the broadest sense, that political civilisation depends absolutely on the rule of law. But in general it is better for society if the sphere of politics is recognised as being largely distinct from that of law.

Politics is a rough game. It has its own rewards (fame, office) and its own punishments (disgrace, electoral defeat). If it becomes customary for unelected authorities – police, bureaucrats, judges, “independent” regulators – to intervene against political acts, those authorities become, in effect, political.

That spoils their real value and gives them a job for which they lack legitimacy, because they are not elected.

It was in my view – though I respect many friends who think differently – outrageous and dangerous when, in 2019, Lady Hale put on her spider badge in the Supreme Court and told the Prime Minister that Parliament could not be prorogued. The arachnid tentacles of law had reached out to wrap their gossamer round the political process, acting politically as they did so. The ensuing general election result proved that the court’s action had been self-defeating.

In public life, by far the greatest quantities of ordure are thrown upon MPs and ministers. Rightly so, in that they make the laws and, in the latter case, are ultimately responsible for running the country.

But there is nevertheless something weird about the venom we direct at them. They are the people elected under a system which we endorse by voting, even if other voters choose candidates we do not want. I worry that such anger blinds us to the advantages of being ruled this way, rather than by a permanent elite of people in law, administration, policing, education and so on, whom we can neither appoint nor dismiss.

In politics, it tends to be the extremes of Left and Right who most readily muddle up law, police and politics. The Right, often visible at Conservative Party conferences of yore (less so today) were always wanting to lock up criminals, “hooligans” and so on, “and throw away the key”.

In recent years, the Left has imitated the Right, but with different purposes. It has shifted from merely attacking the police and the legal system to trying to co-opt them for its political and cultural aims. Hence the constant pressure on them to believe self-declared victims of racism, paedophilia, homophobia, sexual assault etc without the evidence that a court requires.

Hence, too, the development of the idea of a “hate crime” (as if almost all sorts of crime did not involve hatred, or at least contempt). With that idea comes pressure on the police to identify allegedly bad words spoken by members of the public and prevent them being said or to bring the perpetrators to punishment.

Perhaps the greatest problem with wokery is not its specific beliefs, but its detestation of freedom of speech. It is skilled at finding ways of institutionalising this detestation.

There should be much closer study, for example, of how HR departments in companies and public services now police the words and actions of employers and employees alike. More and more, bodies other than Parliament are policing our conduct, perhaps even our thought.

In this context, we should revive interest in the concept of “parliamentary privilege”. In current parlance, the word “privilege” means a bad thing – helping the rich and powerful against the weak. Parliamentary privilege means almost the opposite and was hard fought for. It means the right of Members of Parliament that, as the late 17th century put it, “the freedom of speech and debates or proceedings in Parliament ought not to be impeached or questioned in any court or place outside Parliament”.

It is worth defending the freedom and primacy of politics, even if, as in Boris’s description of some new accusation against him, so much of it is “total rhubarb”.