'ONE sudden infant death is a tragedy, two is suspicious and three is murder, unless proven otherwise." This is Meadow's Law. On first hearing it sounds almost glib, vaguely reminiscent of Oscar Wilde, but for the innocent mothers jailed for murdering their babies, its consequences have been devastating.

Professor Sir Roy Meadow, the expert who propounded the 'three strikes and you're out' theory, was one of Britain's leading paediatricians and for more than 20 years his observations went almost unchallenged. Highly respected, he was much in demand as an expert witness in cot death cases, but in 1999, his reputation took the first of a series of blows that would eventually leave it in tatters.

Sir Roy was called to give evidence against Sally Clark, the Cheshire solicitor who was convicted in 1999 of murdering her two baby sons. In court, he said the chances of two children in the same family dying of cot death were 73 million to one. It was later discovered that he had lifted the figures from a draft copy of a report into cot death before it was even published.

Mrs Clark's conviction was overturned last year, when the law lords described his evidence as "grossly misleading". His claim was also hotly disputed by the Royal Statistical Society, which wrote to the Lord Chancellor to say there was "no statistical basis" for the figure. In fact, recent research suggests that genetic factors make the odds as short as 64 to one.

But despite the controversy, Sir Roy was hired as an expert witness in the case of chemist Trupti Patel. He told the court that cot death did not run in families, despite the fact Mrs Patel's grandmother had lost five babies. She was found not guilty of killing her three children.

In December last year, Wiltshire shop assistant Angela Cannings appealed successfully against her conviction for murdering her two sons. The case called into question the reliability of expert testimony and sparked a massive inquiry into the cases of 258 women convicted of murdering their babies. The review will also look at the cases of parents - as many as 5,000 - whose children were taken into care because of fears they might harm them.

It has taken time but the era of Meadow's Law is now over. The dictum, which was adopted by doctors, police and lawyers, was so powerful it created an attitude of suspicion that effectively shifted the burden of proof onto the accused. Sir Roy himself is now in the spotlight. He is effectively banned from giving evidence and is under investigation by the General Medical Council. But is he the villain he has been made out to be?

Now 70, Sir Roy lives in a large red brick house in the village of Weeton, near Harrogate, in North Yorkshire, with his second wife Marianne. Two cars are parked in the drive but no-one answers the door, and the phone rings and rings.

It seems Sir Roy is avoiding the press - and not surprisingly. Since Angela Cannings' appeal, it seems to have been open season on the man who was once the face of paediatric medicine in Britain.

When rumours began to circulate that his portrait was to be taken down from the walls of the Royal College of Paediatrics, president Professor AW Craft wrote to the Daily Telegraph defending his colleague, saluting his "courage" and calling on the press and public to appreciate the importance of child protection work, citing the case of Victoria Climbie.

Other supporters have referred to him as a man of great skill and compassion and certainly, until recently, there were very few who would criticise him.

One was Jean Golding, professor of epidemiology at Bristol University, who has examined the role played by genetic factors in cot death. "He just seems convinced it is going to be murder whatever the case," she said.

Educated at Wigan Grammar School and Worcester College, Oxford, Sir Roy first became interested in child health while working as a GP in Banbury, in Oxfordshire.

He then moved to Leeds University as a senior lecturer and was offered a chair in paediatrics and child health in 1980 at the city's St James's Hospital. He remained there until his retirement five years ago.

For the last 20 years, Sir Roy has been a leading figure in paediatric medicine. A former president of the British Paediatric Association, he was knighted in 1998 for his services to child health.

He came to prominence in 1977 when he published a paper in The Lancet about a condition he named Munchausen's Syndrome by Proxy - a form of child abuse where a parent harms a child to draw attention to themselves.

In 1993 he worked on the high profile case of Beverley Allitt, a nurse who murdered four children and harmed several others. It cemented his growing reputation, confirmed his position as a leading expert witness, and for the last few years he has been commanding fees of between £3,000 and £5,000 every time he produces a trial report.

His work on Munchausen's Syndrome by Proxy has proved controversial. Some regard it as invaluable, while others criticise it vehemently. Earl Howe, the Opposition spokesman on health in the House of Lords accused him of failing to back up his theories with evidence and described his work as "one of the most pernicious and ill-founded theories to have gained currency in childcare and social services over the past ten to 15 years".

But the evidence of an expert witness alone cannot convict and Sir Roy was just one of several experts in the cases in which he appeared. The Court of Appeal decision to quash Sally Clark's conviction, for example, did not hinge on his testimony but the fact that crucial evidence from a pathologist had not been made at the original trial.

Nevertheless, his theories seem to have created an atmosphere of suspicion and became a powerful tool in the hands of the prosecution. White-haired and softly spoken, Sir Roy has been described by friends as "sober and serious". His delivery of evidence in court is said to have been dispassionate, even dull, but it was clearly compelling, and Meadow's Law was a memorable soundbite that became a rule of thumb. It was a rule of thumb that helped convict Sally Clark and Angela Cannings, and perhaps many more innocent women.

Some mothers do abuse or kill their children and Sir Roy's evidence may have helped to convict them. His work has certainly drawn attention to a major issue and no one is questioning his motives, only his methods, his severe outlook and sweeping statements.

The police, medical and legal professions were all quick to subscribe to Sir Roy's theories, seemingly without question. Now he has been discredited, the women who have been wrongly convicted can hope for justice - but it will be little consolation for the years they have spent behind bars.