A cornerstone of any -functioning democracy is the separation of police and the courts on one hand, and government and parliament on the other. Where the latter are charged with making the law, they should never, ever be allowed to interfere with the enforcement of that law. Politicians have no power to tell the police what to investigate. As Lord Denning once observed, no policeman is subject to orders of the Secretary of State: ‘No minister of the Crown can tell him that he must, or must not, keep observation on this place or that. Or that he must prosecute this man or that one… He is answerable to the law, and to the law alone.’

In Britain, for most of the time, that separation has been respected. Prime ministers, leaders of the opposition and others with political power do not pick up the phone to Scotland Yard and demand that someone — their political opponents, for example — be investigated and prosecuted. But in recent years, we have had a breach between lawmakers and law enforcers. Tom Watson, then a Labour MP, worked out that if you accuse police of a cover-up you can make them panic, and persuade them to investigate your opponents. His first success was over phone hacking. He then moved on to paedophilia.

To no one’s surprise, the Independent Inquiry into Child Sexual Abuse (IICSA) has found that the ‘Westminster paedophile ring’ that Watson described in the House of Commons did not exist. The ‘clear intelligence’ he referred to turned out to be wild conspiracy theories. The claims that young boys were procured for the gratification of the former prime minister Sir Edward Heath and his colleagues before being strangled or knocked down by cars were concocted. That much became clear with the conviction last year of Carl Beech, the convicted paedophile whose outlandish allegations led to the setting up of the inquiry in the first place.

But the wonder is how Beech’s fantasies were ever allowed to get so far, culminating in an inquiry which has cost taxpayers £150 million. Police are bombarded with such fantasists all the time. The difference was Watson’s tactics: he used social media to whip up a storm and see if the police and prosecutors would buckle. They did — with the result that the names of Leon Brittan, Lord Bramall and others were dragged through the mud.

The IICSA has not been entirely without purpose. It has shown that in the 1970s, police and other authorities were lax in bringing paedophile politicians to justice, and sometimes did not act when they could. It emerged, for example, that the Lancashire constabulary investigated Cyril Smith’s abuse of children in a Rochdale home in 1969 — three years before Smith became an MP. Smith even admitted that allegations made by boys were true, but they took no action. He went on to serve 20 years as an MP and to receive a knighthood. But the idea of an ongoing cover-up was a fantasy.

Police and parliamentary authorities, having been embarrassed by their failure to act in historic cases, were swept up in a sense of panic and felt the need to show that they took allegations of sexual abuse by powerful figures seriously. Even that, however, does not explain why the Metropolitan police told reporters that Beech’s allegations were ‘credible and true’. They weren’t the only force to be taken in: Wiltshire’s chief constable Mike Veale said he believed allegations against Sir Edward Heath ‘120 per cent’. Aside from the fantastical nature of Beech’s claims, surely it ought to be obvious to the most junior of police recruits that describing any allegations as ‘true’ is prejudicial to a subsequent trial?

The 18-month investigation into the Westminster allegations stands as an object lesson in how not to carry out a police investigation. Officers dangled the names of well-known figures before the public in the hope of attracting more ‘victims’ to come forward — when they should have known they would attract fantasists and gold-diggers. Suspects were left in limbo long after it should have been clear that there was no proper evidence against them.

In the space of a generation we seem to have gone from a society in which people making accusations of child sexual abuse were routinely dismissed as liars, to one in which they are believed automatically. People who make accusations are referred to as ‘victims’ before their allegations have been tested in court. This is not a good foundation for justice. The accusers should be treated with respect and their allegations investigated, but their word should not be favoured over that of the accused.

For the past ten years institutions which should be reasonable and impartial have been infected with moral panic. The police have succumbed to hysteria, as has the Church of England — which behaved disgracefully over allegations against the late Bishop Bell. It was as if both the force and the Church felt they hadn’t taken abuse allegations seriously in the past, and must make up for it. Politicians and the media often whip themselves up into a frenzy. The lesson of the past decade is that the police and prosecutors should be immune from it.