It is, I grant you, a plea likely to fall upon a deaf national ear: that Chris Langham, acknowledged enthusiast of grotesque imagery of children, is in fact a victim of injustice. When a man has just been found guilty of downloading abusive pornography, thus surely establishing himself as — at least — a sleazy fool, it is tempting to decide that nobody should care further; throwing away the key, indeed, becomes attractive.

Nevertheless, if we are to consider the charges upon which he was convicted, it is only right to consider the greater charge upon which he was not: the sexual assault of a teenage girl. To anyone who followed the trial, it was obvious from the start that she, now an adult woman of 25, was selling fantasies at best or porkies at worst; no jury was ever going to buy them and it would be astonishing if the police and the Crown Prosecution Service did not know that. It is fair, then, to ask why they brought the assault case at all – and to conclude that, on the evidence available, it was cynical manipulation designed to guarantee a hostile jury for the other charges.

Her testimony would not prove her own claims. But it would ensure that the jury was exposed to a drip-drip recitation of “grooming” and “underage” and “paedophile”; they would hear an admission by the defendant of sex when he was 50 and she 18 — not illegal, but adding to the pervy feel; they would be told that her evidence supported the proposition that Langham had a generally unhealthy interest in young girls (if that were a pattern in his life, where are the others?) — and, most of all, it would beget a useful blurring of the otherwise mitigating distinction between looking and touching.

For the police, especially in succulent cases involving the famous, it is increasingly easy to find such a handy helpmate. It starts with trawl by avid media: make sure that when Pete Townshend is driven off, the paparazzi are at hand; when Jonathan King is questioned over allegations subsequently withdrawn, it is leaked to the tabloids; when Matthew Kelly is arrested, it happens in a filled theatre; when Chris Langham is charged, it coincides with an awards ceremony where he was tipped, correctly, to win.

The rest takes care of itself: out from the woodwork crawl the snipers and the vipers, each busting guts to help the CPS to bolster potentially wobbly prosecutions. Facts don’t come into it. The nature of most of these cases means no witnesses, no evidence, no forensics; allegations are frequently carbon-dated – King’s went back 30 years, as did Kelly’s, and Langham’s nearly a decade – so one word against another is all there is. If the anonymous accuser is not believed, he or she has lost little but time and theatrics; if he or she is, the rewards are great and, crucially, calculable before the trial begins.

Criminal compensation is awarded according to published tariff; you can actually look it up to see how much for oral sex, how much for intercourse, how much for buggery — so if there is to be no supporting evidence anyway, the incentive is clearly to go for broke. Meanwhile, agent purveyors can tell you, in advance and to the penny, the eventual return for waiving anonymity and flogging the sorry tale to a panting Sunday rag . . . if, that is, you manage to be convincing enough in court. Langham’s friend failed to be; the next one might.

The bigger pity, of course, is not just that a minx makes money. It is that in this mutually back-scratching collusion of interests, between alleged victim and instruments of prosecution, it is truth that is the first casualty. And anyone who thinks that the greater good is still served by helping to lock away a bad or weak or troubled man like Langham might spare a second thought for someone like Kelly: wholly vindicated, on all counts, yet with his life and career savaged. He said at the time: “If you don’t have your name, you don’t have anything”; today, four years on, friends say he will ache for the rest of his life.

Is there a simple answer? I wish. But we might start by addressing what is an elemental, systematic problem in this area of justice. Perhaps we revisit the idea of anonymity for the accused, under which Langham would still be forever remembered for pornography but not, as he surely now will be, also as a rape suspect.

Perhaps we relax the rigidity of fixed compensation tariffs, leaving more flexibility for a judge who knows a chancer when he meets one. Perhaps we beef up the rules on chequebook journalism, including hurling bricks upon any hint of a “deal”, on or off record, before trial. Most of all, we should stop the bundling of dissimilar charges; viewing pornography has nothing to do with sexual assault, and nobody is served by pretending otherwise.

Next time the lawyers of the CPS have a witness such as the woman who testified against Langham, let them prosecute if they think they can win in a stand-alone trial. Failing that, they — and she — should button a lip; the notion that ends justify means might have visceral appeal, but it has no place in law.

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