A General Medical Council hearing has struck Professor Sir Roy Meadow off the medical register after finding him guilty of giving erroneous and misleading evidence in the Sally Clark case. So what does the future hold for expert witnesses?
Sir Roy was a pivotal expert witness
They are drawn from specialisms and are skilled in a field of expertise - be it ballistics, forensics, engineering, medicine or statistics. There are hand-writing analysts and lip-readers.
Expert witnesses can earn a solid supplementary income - they are employed by lawyers on behalf of their clients - and they are there to illuminate complex issues that come before the court.
But that is at odds with the scrutiny aimed at Professor Sir Roy Meadow and fellow paediatrician Professor David Southall.
The murder convictions of Sally Clark and Angela Cannings were overturned after failures in expert witness testimony. A review of 300 infant death convictions follows and the Court of Appeal is hearing the cases of four people convicted of killing or harming babies.
If they are cleared, about 90 other cases could be challenged.
Problems with expert testimony are not confined to the medical arena.
The BBC's Newsnight revealed how the credibility of one lip-reader has been undermined. The CPS will no longer use her to analyse what people caught on silent CCTV are saying and cases may be reopened.
In a 2004 retrial, a man was cleared of murder after being convicted on expert testimony of ear-print evidence - later undermined.
Prosecutions, appeals and compensation come at the expense of the taxpayer and the system's credibility.
So why involve expert witnesses? "The expert is there as an extension of the judges know-how," says Tom Magner, forensic expert witness and spokesman for the Society of Expert Witnesses.
Rules governing their use in civil trials were introduced in England and Wales in 1999 as Lord Chief Justice Woolf wanted to address rising costs and time taken. Pay limits and an increasing use of jointly-appointed experts were among reforms.
Change there has not come without problems: A September 2003 Law Society survey of 12,700 firms found the majority were happy with single joint experts but more than half also had difficulties.
Some feared the system's credibility was devalued by a poor quality expert and they could decide a case without a full understanding of the legal issues.
"If one got it completely wrong, how would we know, what can be done about it?" asked a respondent.
Who you know
But it is in criminal cases that the high-profile failures in expert witness evidence have come.
Their rules are under review by the Criminal Procedures Rule Committee, set up in 2004. The Home Office's Office of Criminal Justice Reform is also looking at changes.
While the court decides if experts can appear, who is picked to take that role is not regulated.
Sally Clark was cleared in 2003
Lawyers say when they choose their witness it is about who you know, as well as who has the right expertise.
They select from their contacts, colleagues' recommendations and the raft of witness registers.
For Mr Magner, the failures come from tensions in the system.
In court, the expert is the only witness called to give opinion, rather than facts. And that opinion is on science, which changes, whereas the law seeks certainty.
They are there for the court, but it is the solicitor who pays them.
As a result there is confusion over the role - legal teams have wanted him as a "hired gun" more than a scientist, he says.
"The expert has to not step over the line, he mustn't step into the judicial role.
"Say with slipping by the pool, he can talk about the mechanics of how someone falls down, but can't say how it happened, that they fell backwards or forwards.
"It's a real physical effort sometimes to keep out of the drama."
That view is echoed by Sir Alan Craft, president of the Royal College of Paediatrics and Child Health.
"That's been a big problem, that lawyers have said, 'Come on, doctor, you can be more certain than that, that's not very helpful to us'," he says.
And in his GMC appearance, Sir Roy complained of the "legal jousting matches" that are criminal trials: "You go into the witness box with your mind spinning sometimes."
But for one lawyer, the witness role is clear cut.
"If I call him it's because he can help me get my client acquitted," says Mark Haslam a partner and member of the Law Society's Criminal Law Committee, who uses experts in three quarters of his cases.
But he does admit juries may put too much trust in 'experts'. It is up to the judge, he believes, to direct a jury not just to accept what the expert says.
Reform is under way. And the Meadow case is likely to exacerbate calls for change. So what should change?
Accreditation would help, says Mr Haslam. "That would be a kite mark.
"It would raise the standard and help us instruct people who had substantial experience, who were good and reliable."
But it could also backfire, says Mr Magner, and would not have changed Sir Roy's testimony.
"Good experts think, if I'm going to end up having to do all these things and people are still going to view me in a suspicious manner, why should I put myself up for this?"
The Appeal Court's decision on the four baby death cases may come with new guidance for judges, and the Attorney General's review of convictions could prompt change.
The Royal College of Pathologists and Royal College of Paediatrics has called for greater scrutiny of expert witnesses.
Perhaps English and Welsh courts will take a leaf out of the ancient Scottish law books.
There, the laws of evidence are different. Any crucial fact must be corroborated by two sources, so a conviction could not come on the evidence of one alone.