Defendants are at risk of being wrongly convicted on the evidence of “charlatan” and “biased” expert witnesses, the Government’s law reform body warns today.

A series of highly publicised cases in which convictions have been overturned after concerns over “flawed” expert evidence “represent the tip of the iceberg”, the Law Commission of England and Wales says.

Expert evidence is sometimes admitted too readily and despite several successful appeals over expert evidence, there is a “pressing danger of wrongful convictions”, it warns.

The strong words are unusual from the independent law reform watchdog, which normally couches its proposals in more neutral if not bland language. But they clearly indicate its concern that there is a “real, ongoing problem that demands an urgent solution”.

The problems over the way expert witnesses are used in courts and how lay juries can be expected to weigh them has been fuelled by a series of wrongful convictions.

In recent years, miscarriages of justice such as the cases of Sally Clark and Angela Cannings, both convicted of killing their babies and then cleared on appeal, have highlighted the difficulties.

The commission, an independent law reform body, says there is a danger that juries sometimes have little option but to defer to the views of a particular expert witness. The problem is particularly acute with scientific evidence which is said to have an “aura of infallibility”; jurors might assume that just because it was scientific, it is reliable.

So what does it recommend? First, that magistrates and judges act as gatekeepers and screen expert witnesses by applying a list of criteria, a new statutory test, before they can give evidence in court.

The aim of the test would be to ensure that juries are not swayed by unreliable experts — and the risk of miscarriages of justice reduced. Only evidence that met with the criteria on reliability could be admitted, the commission suggests.

Professor Jeremy Horder, the Law Commissioner leading the project, said: “The parties in criminal trials are relying increasingly in the evidence of expert witnesses. Expert evidence, particularly scientific evidence, can have a very persuasive effect on juries.

“It is vital that such evidence should only be used if it provides a sound basis for determining a defendant’s guilt or innocence.”

The Law Commission report, a consultation paper seeking views on a series of options, says it believes that its proposals would be the “most effective mechanism” for ensuring that “only reliable evidence is placed before criminal juries”.

But it cautions that this reform alone would not provide a panacea because the way scientific knowledge advances means that the problem of expert testimony can never be entirely resolved, as the view at any given time of any hypothesis is subject to change.

There would also need to be other measures: a “more robust approach to the accreditation and regulation of expert witnesses”; a disclosure process under which all parties could screen their opponents’ expert witnesses in advance of trial to assess their experience and qualifications; and training for judges and lawyers on how to assess the viability of a scientific hypothesis.

The commission concludes: “We believe that our proposals, if adopted, would ensure that convictions and acquittals would be founded on expert evidence only if the hypothesis and methodology underpinning that evidence can be shown to be trustworthy.”

And it adds: “We believe that the ‘orthodoxy’ that cannot be shown to be trustworthy should not be admissible.” The absence of any effective screening test risked convictions of the innocent or the acquittal of the guilty.

If that occurs, the commission finally warns, “the perception of justice and the efficacy of the legal system within the community it serves is likely to be seriously undermined”.

Its ideas deserve an airing. People can respond directly, or — in this case — via an interactive online forum (www.lawcom.gov.uk/expert_evidence.htm).

Jurors have spoken of their difficulties of assessing experts and problems still persist with accreditation. Expert witnesses are at the heart of the criminal justice system; its credibility rests on theirs.

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