Expert witnesses are ‘weakest link in English justice system', says wrongly convicted surgeon

The Guardian

15-06-2025

David Sellu knows full well the impact an expert witness can have on the outcome of criminal case, and the lives of the people on trial.
A former surgeon, Sellu spent 15 months in prison after being convicted of gross negligence manslaughter in 2013, following a trial that largely hinged on the evidence of medical expert witnesses brought by the prosecution.
After an appeal in 2016, Sellu's conviction was quashed and the appeal judge criticised the way the expert evidence was handled, saying they 'asserted gross negligence' when this was 'a matter for [the jury] and not the experts'.
'I think I can probably say that there are many, many hundreds of people who would not be alive today had it not been for my skills and my treatment,' Sellu said. 'And yet medicine was deprived of my further input, purely on the back of a case that should never have been brought.
'It's affected my whole family, we've gone through a very difficult time. But we've come out of it all. We're carrying on as best we can.'
He now speaks out about the issues with expert witnesses, particularly in cases involving medical professionals where the subjects being examined are often highly complex and expert witnesses act at the 'crucial bridge' between medicine and the law.
'My case was in 2015, it is now 2025 and I don't really believe that much has changed. It worries me that there will be miscarriages of justice from expert testimony,' Sellu said. 'As recently as the case of Lucy Letby, expert testimony is still being questioned.'
Sellu was convicted over the death of a man at a private hospital in 2010 who suddenly fell ill after knee surgery. The patient's condition deteriorated due to delays to his care, which expert witnesses said amounted to gross negligence by Sellu.
The exonerated doctor said he remained alarmed that there were no 'prescribed training programmes' for expert witnesses to ensure the evidence they give is unbiased, high quality and follows all legal procedure.
'There should be a benchmark that expert witnesses must achieve, because they are such an important bridge between medicine and the law in terms of being able to deliver justice,' he said.
'In my view, they are the weakest link in our justice system. They're not accredited, not properly trained, nobody really knows clearly how they're selected. And they play such a vital role in the delivery of justice that I think it's a shame that nobody has really grappled with this issue to try to get it fixed.'
Expert witnesses are used in almost all criminal trials, but are particularly crucial in medical cases where a jury would struggle to understand and interpret complex terminology.
They are appointed by both prosecution and defence lawyers, and although there is guidance from the Crown Prosecution Service, there is little oversight over how expert witnesses are appointed and what checks are carried out.
One defence barrister said that lawyers often 'don't ask the questions' about the experts they're hiring, and 'work on the premise that people who are purporting to hold themselves out as experts, are experts'.
Sellu said: 'The words 'expert witness' are a bit of a misnomer, because they're neither experts nor are they witnesses. Anybody can put themselves up as an expert witness, there's no clear accreditation.
'And they are the only people in the trial who give evidence who were not there at the time the alleged events took place – they're not witnesses, they're simply giving opinions.'
In 2021 a judge asked the Crown Prosecution Service to investigate an eminent psychiatrist, Dr David Ho, who had been used by prosecutors as an expert witness in a large number of cases, after concerns were raised about him during a murder trial.
In the case of a man accused of beheading his mother, who was found not guilty of manslaughter on the basis of insanity, defence lawyers said there were apparent errors in Ho's report and he allegedly refused to answer questions.
Ho had concluded there was no evidence to suggest the defendant did not know what he was doing, a finding that was disputed by other consultant forensic psychiatrists. The judge said there was concerns that Ho 'had potentially lost the necessary degree of independence and objectivity, his awareness of his overriding duty to the court, and his approach to his task'.
The CPS said an internal review had been carried out, and Dr Ho had not been used as an expert witness since.
There have been a number of high-profile miscarriages of justice linked to inadequate medical expert evidence. Three men found guilty of murder in 1998 had their convictions quashed due to 'discredited' evidence by pathologist Dr Michael Heath, whose findings were questioned in a string of cases.
Despite the concerns around the veracity of his work, he continued to practise and was under investigation by the General Medical Council at the time of his death in 2023.
In the 1990s, evidence by paediatrician Sir Roy Meadow led to several wrongful convictions of mothers for murdering their babies. Sally Clark, Trupti Patel and Angela Cannings were all exonerated after evidence by Meadows, used as an expert witness by the prosecution, was proven incorrect.
He misused statistics to convince a jury it was almost impossible for more than one sudden infant death to occur in the same family, and that it was much more likely to be murder.
'There is a real danger with expert evidence, because it is elevated evidence, so when it's wrong, it can lead to wrongful convictions and that's a real concern,' said Matt Foot, co-director of Appeal, which supported Sellu's case.
'Where the problem comes, and it has happened in many miscarriages of justice, is when expert evidence is given that is biased, inappropriate, or completely unreliable.
'Experts are not there for the police or the prosecution. They can feel obliged to provide evidence in a certain way when their duty is to the court for independence rather than to any party. That's the biggest danger, I think, because that danger leads to innocent people going to prison.'
Expert witnesses are often also crucial in overturning miscarriages of justice, he said, but greater regulation or oversight would be beneficial.
'When things go wrong, there is no proper record anywhere that it has happened, and that you therefore need to treat this expert with great caution,' said Foot. 'That's not part of the system. So there are no safeguards in place to stop that happening again, with the same person.'