For years, paediatricians turned a blind eye. In the absence of corroborating evidence, no charge of murder had a chance of being proved.

Then, 20 years ago, Münchausen’s syndrome by proxy emerged in Britain, the condition in which parents deliberately harm their children to draw attention to themselves. Since the syndrome was first described, more than 200 papers have appeared in the medical literature.

It was important because it provided the intellectual underpinnings to explain the inexplicable. Psychiatrists and paediatricians became more confident in asserting that some cot deaths were indeed murders.

They concentrated on cases where parents had apparently suffered a string of cot deaths. Where two or three children had died, it seemed more reasonable to believe that the mother was responsible.

Some professionals urged doctors and law-enforcement authorities to “think dirty” whenever a baby died suddenly and unexpectedly. The move to provide ever-greater protection to children fuelled the change and cases began to appear in the courts.

At the heart of the process was Sir Roy Meadow, a child-care specialist and proponent of Münchausen by proxy, who appeared as an expert witness in many cases, including the Clark, Patel and Cannings cases.

In support of his belief that many cot deaths are in fact murders, Sir Roy cited the cases of 81 children judged by the courts to have been murdered by their parents.

In 49 cases, these deaths had initially been classified as cot deaths, while 29 were classified as deaths from natural causes. Nearly half had been admitted to hospital for unusual or unexplained events, and discharged within a week of their deaths.

Sir Roy’s confidence made him useful as a prosecution witness. But his real expertise was not in psychiatry, but paediatrics. In the Cannings case, he said that the abrupt changes in the health of the babies — perfectly well one moment, dying or dead the next — were consistent with smothering.

It was unusual, he said, for a child’s health to deteriorate so rapidly as a result of infection or disease. Other witnesses were called who gave different opinions.

The Court of Appeal verdict does not call into question Münchausen’s syndrome by proxy but it does suggest that,where opinions differ and science is moving fast, experts should not be too confident of their own judgment and juries should not be asked to choose between them.

Alan Williams, the Home Office pathologist, is under investigation. He failed to disclose that one of Sally Clark’s children was infected with bacteria that could have contributed to his death, a failure strongly criticised by the appeal court judges who eventually freed her.

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