It is the oldest trick in the book. You snatch a politician's mildly controversial remark. You eradicate context and qualification and invite rent-a-quote to be subject of the verb "to slam" or object of the verb "to infuriate". You then get the leader of the opposition to demand a sacking, and stake out the victim's house to see how he takes it.

Ken Clarke's spot of bother over rape sentencing this week has been a classic. His suggestion that not all crimes within a category are necessarily identical is almost trivially obvious. But who cares when the political heat is on and the mob is running hotfoot to the guillotine? It does not want obvious, it wants blood.

Retributive justice went downhill from the moment in 1215 when Pope Innocent III did away with trial by ordeal and replaced it with torture. Out went the sophistication of half-drowning, flesh sizzling and trial by choking "on the blessed morsel". In came hi-tech sadism. As a result, the blood-thirsty extraction of a confession was substituted for the priestly inspection of wounds as proxy for justice. Records suggest that half of ordeal victims secured acquittal. That rarely happened after torture.

Clarke's roasting by the tabloids on Wednesday suggests that Britain is moving from trial by ordeal to sadism. Women commentators cried for his political castration if not execution. How dare he suggest rape sentences should reflect the severity of the crime? How dare he suggest that his critics merely "want to add a bit of sexual excitement to the headlines"? In went the familiar boot: even if Clarke was right he was insensitive to the feelings of victims and therefore wrong. In the new politics, government is not about doing the right thing. It is about not hurting anyone's feelings, even if they are not really hurt.

Sentencing policy in Britain is stupid, sending more people to worse jails with less sense of purpose than in any other developed and civilised country. There were 10,000 prisoners in England and Wales between the wars, against 85,000 today. The reason is that every time any crime is mentioned, the press and public opinion go barking mad. There is no local accountability for policing or communal discipline, and no localism in the prison regime. Punishment in Britain is a monolithic, primitive nationalised industry.

Anyone who injects an iota of complexity into the debate, be it on drugs, rape, violence or youth crime, is shouted down and told to "think of the victims". British justice thinks only of past victims, never future ones. I am sure Clarke is now being told to heed this lesson, and that it should serve as a warning to any future justice minister who dares to apply reason to penal policy. You will be tortured if you do.

Those in British public life have long been subject to trial by ordeal. Currently starring on the hot coals roadshow are Clarke and the Lib Dem energy minister, Chris Huhne. They follow David Laws (on expenses), Vince Cable (on Murdoch), Caroline Spelman (on forests) and David Willetts (on university fees). They in turn follow Tessa Jowell, David Blunkett and Peter Mandelson among many others in the last government. It does not matter if the gaffes and mishaps are political or personal. To the jackals, any wounded buck is worth a hunt.

In each case the ordeal is the same. Cameramen slide silently into place outside the domestic front door. Telephoto lenses are trained on upstairs windows especially if, please God, the mishap has to do with sex. Any sign of life is greeted by a fusillade of flashes and such erudite questions as "When are you going to say sorry?" or "Have you stopped cheating on your wife, you love rat?" Just getting to work involves a fixed grin, a fumbling for keys and trying to drive away with dignity from a shrieking horde in full view of one's neighbours.

None of this adds light to British politics, but it is not meant to do so. It is meant to show the lords and masters that, in the last analysis, the mob is sovereign. The ordeal continues until the public cannot stand more pictures of Clarke or Huhne getting in or out of a car. Judgment then takes the form of the BBC's political editor declaring that "the prime minister feels" that he either can or cannot tolerate the victim's "error of judgment". This concludes the matter, like a medieval priest inspecting the wounds.

In a heavily centralised democracy with a wholly ritualised parliament, trial by media ordeal is the only way we have to keep our governors on their toes. They are now pleading for a privacy law, supposedly to mark out that elusive divide between what is in the public's interest and what is of interest to the public, between accountability and prurience. The 1990 Calcutt inquiry (on which I served) concluded that defining "public interest" for the purpose of privacy had two disadvantages. It would be a make-work scheme for lawyers and, since media intrusion was mostly about sexual or corporate misbehaviour, curbing it would be merely an exercise in aiding the rich and powerful. This was hardly a function of the law or a national priority.

The attempt of the high court to guard privacy through court injunctions, whose tiers of secrecy were pioneered by another Calcutt member, Mr Justice Eady, began to crumble yesterday, with the lifting of the privacy injunction awarded to Sir Fred Goodwin. It had become obsessed with the sexual antics of celebrities, vastly entertaining judges, but bleak for the rest of us.

Being hounded by the British press is one of the most unpleasant experiences short of physical assault. It is the tax that a free society imposes on celebrity. In the case of politicians it is an ordeal which they must undergo as the price of office, indeed they must in some degree anticipate it. Those who go into public life must possess a strain of masochism. When the ordeal is unfair it should be regarded as just one of life's nasty accidents. When it is disproportionate punishment for a mishap, gaffe, peccadillo or insensitive remark, it is crude accountability. The justification is perhaps that it may compensate for more serious offences that pass unpunished. If we cannot nail a minister for wrecking the economy, at least we can get him for adultery.

Either way, trial by media ordeal is the best rite of passage we have for whether politicians can stand the heat. It is Tamino's test in the Magic Flute. If someone cannot fend off the press, how will they face down the lobbyists, apparatchiks and thugs of modern government?

Clarke is an old hand at this game. He just needs to keep his head and not show it hurts. When Downing Street's ghouls come to inspect his wounds over the weekend, he seems likely to survive. As the blood dries, the press will go in search of its next victim. But terrible damage will have been done to the cause of penal reform.