The present article, “Is the treatment of expert witness evidence in English Law fit for purpose in the 21st Century?” shall look into the issue of expert witness evidence in criminal proceedings in the UK. The use of expert witness evidence in the United Kingdom (‘UK’) is based on the position that experts are required to translate and… Read More »

The present article, “Is the treatment of expert witness evidence in English Law fit for purpose in the 21st Century?” shall look into the issue of expert witness evidence in criminal proceedings in the UK. The use of expert witness evidence in the United Kingdom (‘UK’) is based on the position that experts are required to translate and educate relevant aspects of their areas of expertise such that the jury can better assess the evidence to which it relates. However, in recent...

The present article, “Is the treatment of expert witness evidence in English Law fit for purpose in the 21st Century?” shall look into the issue of expert witness evidence in criminal proceedings in the UK.

The use of expert witness evidence in the United Kingdom (‘UK’) is based on the position that experts are required to translate and educate relevant aspects of their areas of expertise such that the jury can better assess the evidence to which it relates. However, in recent times, critics have argued that the use of expert witnesses in criminal procedure is obsolete because juries may show deference to the expert views and dismiss their own valid opinions, inter alia other concerns.


What is expert witness evidence?

The conceptual justification for expert witness evidence in criminal justice proceedings is for the members of the jury or judges to attain a better understanding of concepts in specialized areas that laypersons could not be expected to understand, in order to make an informed decision as to the guilt of an accused.

This could include a preliminary understanding of forensic, medical, psychological concepts and doctrines in order for jury members to assess, understand, and appreciate the significance of certain evidence while disregarding other irrelevant details.

What is the scope of expert witness evidence in the UK?

According to the Law Commission of the UK,[1] there are three factors relevant in considering the admissibility of expert witness evidence. This was discussed by King CJ in the Australian case of Queen v. Bonython.[2] As a part of the larger body of common law, these factors while being laid down in an Australian court are also part of common law in the UK (i.e England and Wales). They are as follows:

  • Subject-matter beyond the common knowledge of jury member

According to this, the consideration is whether the subject matter of the opinion without any formal instruction in the specialized area of knowledge or practical experience would be capable of formulating an informed, sound judgment without the assistance of a witness in so possession of special knowledge or experience in the self-same area.

  • The subject matter is a recognizable, concise discipline

The consideration here is whether the opinion is part of a body of knowledge or practical know-how that is recognized or structured to be accepted as a reliable discipline or body of knowledge, relying on which the jury could form a valid opinion regarding the criminal intention of an accused in a criminal trial.

  • The expertise of the expert witness

The above two factors are not sufficient to consider the admissible nature of the expert opinion, rather it is also necessary to consider whether the expert in question has the sufficient qualifications and study required to produce an opinion of value to the court, which would thus aid the jury members.

  • Impartiality of the expert witness

Another consideration is that the expert must provide an impartial opinion. This consideration is at the heart of contemporary concerns regarding the admissibility of expert opinions. The overriding duty of the expert is to that of the court, and the expert should not make decisions that prejudice the evidentiary value of his/her opinion in favor of the party that has called him/her to testify.

Problems with expert witness evidence

While the requirement of expert witnesses is no doubt imperative for educating jury members as to aspects of specialized fields, it is also possible that the jury members may be deferential to the knowledge of the expert when it comes to disputed questions of fact.[3] Thus, there are questions being raised as to the admissibility of expert witness testimony and whether there is a requirement for this practice to continue in the contemporary era of a criminal investigation where forensic analysis has arguably rendered expert witnesses redundant.

Structure of the paper in parts

The present article shall discuss expert witnesses in the English common law system. The first part shall discuss the development of expert witnesses in justice systems. The second part will present the framework of criminal procedure and policy. The third part shall discuss contemporary problems with the system as it stands.

I. Historical Development Of Expert Opinion In Common Law Justice Systems

  • First recorded use of expert opinion

Folkes v. Chadd[4] (1782) was the first recorded case in England that included an expert witness’s opinion as evidence, and hence also laid down the seminal rules on the admissibility of expert opinion as evidence in the common law. Also known as the Wells Harbour case, the cause of action was civil in nature with the court adjudicating on whether the silting of the seaside town Wells Harbour in Norfolk constituted a public nuisance or not. The court permitted a civil engineer known as John Smeaton to provide his technical and scientific justification to aid the adjudication of the case.

In the words of Lord Mansfield J.,“…the cause of the decay of the harbor is also a matter of science, and still more so, whether the removal of the bank can be beneficial. Of this, men such as Mr. Smeaton alone can judge. Therefore we are of the opinion that his judgment, formed on facts was very proper evidence”[5]

Thus, the Folkes case is cited as the seminal source of rules and the practice of expert opinions in common law, including civil and criminal proceedings. This rule has also been the leading case in the United States (‘US’) courts, with the judgment being quoted extensively in related cases, as mentioned by the Chief Justice of the New York Supreme Court in Lincoln v. The Saratoga and Schenectady Railroad Company.[6]

The famous M’Naghten’s case[7] which laid down the rules on insanity known as the M’Naghten’s test, also confirmed the importance of expert opinions in specialized issues. In this case, the defendant shot and killed the victim under the belief that the victim was part of a criminal conspiracy to murder him. At trial, the defendant was acquitted due to his claim that he was suffering from insane delusions at the time of the impugned action.

Chief Justice Tindall in his judgment noted that wherein facts were disputed, courts needed the expertise of a trained professional or expert in the field to provide hypothetical questions in better understanding the issues in a case, in cross-examination.

In his words, “…In our judgment, counsel calling an expert should in examination-in-chief ask his witness to state the facts upon which his opinion is based. It is wrong to leave the other side to elicit the facts by cross-examination. ”[8]

  • Daubert case and impact on common law rules on expert opinion

The development of admissibility of evidence in the US had a far-reaching impact on other common-law jurisdictions outside the US. In Frye v. the United States,[9] the admissibility of systolic blood pressure evidence obtained through the use of polygraph testing was considered, at a time wherein polygraph testing was ruled to be inadmissible.[10] In this case, as polygraph testing was not generally accepted as reliable evidence in the wider scientific community, the evidence was ruled to be inadmissible evidence.

Following this, the Federal Rules of Evidence in 1975 were enacted in the US, which set out explicit standards for the admissibility of expert evidence in federal courts.[11] Rule 702,[12] which largely is echoed by the Australian court in Queen v. Bonython,[13] as mentioned above speaks to the rules of evidence relating to testimony by expert witnesses in the US.

However, the position taken on expert evidence was suitably modified by the judgment in Daubert v. Merrell Dow Pharmaceuticals[14] in 1993. The facts of this particular case are as follows: Jason Daubert and Eric Schuller were born with serious congenital defects. The parents of the children duly instituted a case against Merrell Dow Pharmaceuticals contending that a particular drug was manufactured by their parent company, Dow Chemical Company.

However, the contentions of the petitioners were rejected at the trial and appellate court stages as the submitted expert evidence was based on methodologies that were not yet accepted within the scientific community. This principle was applied in another case, Kumho Tire Co. v. Carmichael (1999)[15] wherein evidence from a technician (versus a scientist) was deemed inadmissible. Thus, Daubert is the locus classicus on expert evidence in the US and also has influenced common law adjudication in other jurisdictions outside the US.[16]

More recently in the Turner case (1975)[17], it was stated the function of the expert was to supply information and knowledge that was outside the expected knowledge of a judge or jury member. Accordingly, it was stated in that case:

“An expert’s opinion is admissible to furnish the court with … information which is likely to be outside the experience and knowledge of a judge or jury. If on the proven facts a judge or jury can form their own conclusions without help, then the opinion of an expert is unnecessary.”[18]

II. Framework- Statutes Dealing With Admissibility Of Testimony Provided By Expert Witness

The UK justice system follows common law, wherein precedent and the doctrine of stare decisis guide the appreciation of expert opinion witnesses.[19] This implies that codified rules are not given undue priority when compared to past precedents, which are construed to be more authoritative in value. Nonetheless, given as the admissibility of expert testimony requires objective standards, certain statutes do codify such factors. Some such statues are given below.

  • Criminal Justice Act, 1988

Section 30 of this Act, which is concerned with criminal proceedings in the UK, deals with expert reports. According to sub-section (5) of Section 30, the expert report is defined as a “written report by a person dealing wholly or mainly with matters on which he is (or would if living be) qualified to give expert evidence.[20]

In essence, the section states that any expert opinion shall be admissible evidence in criminal proceedings regardless of whether the expert himself/herself actually presents oral evidence of that nature.[21] Further, the court’s permission is required for a case wherein the expert shall not give such oral evidence.[22] This section also provides the factors to be considered by the court when giving such leave or permission as aforementioned:

For the purpose of determining whether to give leave the court shall have regard

  1. To the contents of the report;
  2. To the reasons why it is proposed that the person making the report shall not give oral evidence;
  3. To any risk, having regard in particular to whether it is likely to be possible to controvert statements in the report if the person making it does not attend to give oral evidence in the proceedings, that its admission or exclusion will result in unfairness to the accused or, if there is more than one, to any of them; and
  4. To any other circumstances that appear to the court to be relevant.”[23]
  • Criminal Procedure Rules, 2020

Rule 19 of the Criminal Procedure Rules, 2020 deals with the expert’s duty to the court and comprehensively lays out the various obligations expected of an expert in court. These include giving objective and unbiased opinions which is within the expert’s area[24] as well as complying with court directions and informing the court of other experts’ failure to take required steps.[25]

Critically, sub-section (2) of Section 19(2) states explicitly that “This duty overrides any obligation to the person from whom the expert receives instructions or by whom the expert is paid.[26] Further, the provision also lays out obligations of the expert to disclose if the expert’s evidence has been commissioned in favor of any party and to inform all parties and the court if the expert’s opinion changes from any written material in statements made beforehand, inter alia other obligations.[27]

III. Problems

The utility provided by expert opinion evidence for the benefit of judges or jury members is evident specialized branches of medicine, physics, mathematics, or science do require an unbiased expert to guide the required persons to perform their stated duties as judges or jury members. However, there are also problems associated with the practice of expert opinion evidence in contemporary times in the UK. They are as follows:

  • Dangers of bias

According to Hand, empirical data may often be misrepresented and can be a cause for bias in expert opinion.[28] The analysis of data itself is a core feature of scientific integrity and when the life, liberty, and property of individuals, groups, and corporations are in question, such data is key to resolving such questions fairly. Subjective decisions risk introducing bias- which may in itself be subconscious, thus creating more opportunities for bias to creep in.

  • The cost of appeals

Unreliable evidence at the trial stage will lead to further costs in the form of legal fees. For the court system, the appellant, defendant, or prosecution authorities, the overall cost is both in terms of time and money. According to official estimates, in 2006-2007 in the UK, there were 3010 pending applications before the Court of Appeal (Criminal Division), with an average of 11 months for appeals against conviction decrees and four months for appeals on sentencing.[29]

  • Wrongful convictions or acquittals

This refers to cases wherein wrongful convictions have been delivered due to incorrect expert opinion evidence and such wrongful conviction has been acknowledged and overturned subsequently by an appropriate authority.[30] On the other hand, wrongful acquittals may lead to repeat offenses, perhaps against the same victim, and is a public health risk.

  • The effect upon public confidence in justice delivery mechanism

In the case of a publicly acknowledged case of wrongful conviction or wrongful acquittal, media attention leads to such miscarriages of justice being widely known. This might lead to the unfortunate result of loss of public faith in the justice system’s ability to perform its function of maintaining law and order. Further, it could preclude or delay members of the public from approaching law enforcement officials in case of any alleged criminal or civil wrongs committed.


The use of expert witnesses in the UK has been a practice that originated in the 18th century and has continued to the modern-day with several adjustments and amendments, allowing for advancements in technological, medical, and forensic evidence gathering. On the policy side, the admissibility of expert witnesses and the evidentiary value of their opinions in criminal and civil proceedings has often been criticized for introducing bias into the minds of judges and jury members alike.

Most criticisms have led to modifications in the evidentiary standards- however, several lacunae do remain at the policy and procedure stage that require ironing out. In conclusion, the practice of expert opinion evidence despite its failings has become an important facet of justice proceedings and fulfills an essential function in the modern era.

[1] Law Commission Consultation Paper No. 190, The Admissibility Of Expert Evidence In Criminal Proceedings In England And Wales: A New Approach To the Determination Of Evidentiary Reliability, Available here

[2] (1984) 38 SASR 45, 46 to 47 (Supreme Court of South Australia).

[3] Supra, at note 1.

[4] Folkes v. Chadd, (1782) 3 Doug KB 157

[5] Ibid.

[6] Lincoln v. Saratoga and Schenectady Railroad Company (23 Wend., 425).

[7] M’Naghten’s Case (1843) 8 Eng. Rep. 718, 722.

[8] Supra, at note 7.

[9] Frye v. the United States, 293 F. 1013 (D.C. Cir. 1923).

[10] Supra, at note 1.

[11] Rule 702, Testimony by Expert Witnesses, Federal Rules of Evidence, 1975.

[12] “A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:

  1. the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
  2. the testimony is based on sufficient facts or data;
  3. the testimony is the product of reliable principles and methods; and
  4. the expert has reliably applied the principles and methods to the facts of the case.”

[13] Supra, at note 2.

[14] 509 U.S. 579 (1993).

[15] 526 U.S. 137 (1999).

[16] Supra, at note 1.

[17] [1975] QB 834, 841.

[18] Ibid.

[19] Stare Decisis, Legal Information Institute, Cornell Law School, Available here

[20] Section 30(5), Criminal Justice Act, 1988.

[21] Section 30(1), Criminal Justice Act, 1988.

[22] Section 30(2), Criminal Justice Act, 1988.

[23] Section 30(3), Criminal Justice Act, 1988.

[24] Rule 19(2), 1A, 1B, Criminal Procedure Rules, 2020.

[25] Rule 19(2), 1B, Criminal Procedure Rules, 2020.

[26] Rule 19(2), (2), Criminal Procedure Rules, 2020.

[27] Rule 19(2), (2), Criminal Procedure Rules, 2020.

[28] D. Hand, Appendix D, Common Sources of Unreliability in Scientific Evidence, N, as cited in Law Commission Consultation Paper No. 190, The Admissibility Of Expert Evidence In Criminal Proceedings In England And Wales: A New Approach To the Determination Of Evidentiary Reliability, Available here

[29] The Court of Appeal Criminal Division Review of the Legal Year 2006 / 2007 (2007) p 18 (Annex A); and also para 1.3, p.3. Available Here

[30] Supra, at note 1.

[30] Supra, at note 2.

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Updated On 7 March 2022 8:20 AM GMT
Devanjali Banerjee

Devanjali Banerjee

West Bengal National University of Juridical Sciences

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