FREE CHAPTER from ‘A Practical Guide to the Use of Expert Evidence in Criminal Cases’ by Richard Padley


What is expert evidence?

Expert evidence is evidence of opinion falling outside the experience of a judge or jury. This contrasts with non-expert evidence that goes to matters of fact. The oft quoted judgement of King CJ in the South Australian case of R v Bonython provides a helpful outline:

whether the subject matter of the opinion is such that a person without instruction or experience in the area of knowledge or human experience would be able to form a sound judgment on the matter without the assistance of witnesses possessing special knowledge or experience in the area; and whether the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organised or recognised to be accepted as a reliable body of such and a special acquaintance with it by the witness would render his opinion of assistance to the court.”1

The Court of Appeal observed in R v Dlugosz and others2 that in determining the issue of admissibility of evidence as expert evidence the court must be satisfied that there is a sufficiently reliable scientific basis for the evidence to be admitted and tested before the jury.

Areas of expertise that practitioners will have often come across involve elements of technical or forensic analysis. These can include:

  • DNA evidence – to assess the likelihood that DNA found on an item of interest has come from a person of interest

  • Psychiatric evidence – to assist establish an individual’s mental state at a particular time of relevance

  • Firearms evidence – in assessing whether a particular item falls within the definitions under the Firearms Act 1968

  • Cell site evidence – to establish location and movement of a sim card

  • Facial recognition – to assess the likelihood that a person shown on CCTV/photograph is the same as a person of interest

However expert evidence is not exclusively based around science or forensic analysis. Areas of expertise perhaps less routinely used have included:

  • Historical facts about Al-Qaeda – Ahmed [2011] EWCA Crim 184

  • The political and economic situation in Russia – Berezovsky v Hine [2011] EWHC 1776 (Ch)

There are however areas where an expert should not stray. It is now well established that an expert cannot go to the question of whether or not an individual is truthful.3 The question of whether a witness is truthful and reliable is a question for the trier of fact and not for the expert.

Additionally, whilst matters of foreign law can often be subject to expert evidence the law of England and Wales is not a proper subject for expert evidence since it falls within the competence of the court.

The evidence an expert gives should be based on admissible evidence, and it is incumbent on the advocate calling the expert to adduce the underlying admissible facts during the evidence.4

Who is an expert?

An expert is an individual who has specialist knowledge in a particular subject area. That specialist knowledge can be gained through years of experience, whether in the pursuit of research and academic study, the practical application of the field of knowledge through work, or often a combination of both.

Qualification can be academic or vocational qualification. Expertise can be gained through ‘on the job’ work, and in some areas of expertise this is essential. Very often experts will have a combination of both academic qualification and practical experience form which they can draw.

In selecting an appropriate expert, the interplay between their knowledge and expertise is a relevant consideration. Whist an expert is entitled to apply their knowledge to reach a conclusion by, for example, referring the academic papers of others in the field5, that knowledge should be evaluated by the expert by reference to their practical day to day experience6. An individual who has a purely academic knowledge of a subject may certainly be described as an expert, but the opinion given by such an expert may well be given less weight with the court than that of a person with a combination of academic knowledge and experience7. That is not to say that academic training cannot engender appropriate experience in the right circumstances.

It is important not to forget that part of the role of an expert witness is to give evidence at court. That itself is something that an expert can receive guidance on. Whilst an individual may well be at the top of their field in respect of their knowledge of the subject area, standing up in a busy courtroom and giving evidence in a manner that can easily be understood by a layman is a separate skill. Practitioners should be aware of their expert’s experience of the courtroom and procedures for giving evidence.

Whilst many profess to have expertise, whether an individual truly does, and whether they hold said expertise in the area relevant to the matters in issue at court are matters that should not slip the mind of the practitioner. It is an important principle that an expert can only give expert evidence in an area within their expertise. This was recently considered in R v Alex Pabon8.

Alex Pabon

Alex Pabon was found guilty after trial of a single count of conspiracy to defraud, in respect of dishonestly rigging the London Interbank Offered Rate (LIBOR). During the course of the trial the SFO relied upon an expert witness, Saul Rowe. Mr Rowe was also used in the retrial of two of Mr Pabon’s co-defendants, Mr Stylianos Contogoulas and Mr Ryan Reich. During the course of the retrial material was revealed to the prosecution and the defence undermining Mr Rowe’s abilities to act as an expert in these proceedings – email correspondence was disclosed that another partner at Mr Rowe’s firm had in fact produced parts of Mr Rowe’s expert report, and text messages from Mr Rowe to others relating to matters on which he was giving evidence.

In summing up the matter to the jury HHJ Leonard QC highlighted the matter within the following passage:

“Despite that catalogue of experience, you may have formed a judgment that he knew very little about the duties of being an expert……he seems to have been perfectly content to sign a standard declaration in which he declared that he had read the Criminal Procedure Rules which govern his conduct as an expert, both before trial and in giving evidence, and the booklet on his duties of disclosure without doing anything really to familiarise himself with either of those documents.

It will be for you to judge whether he has in fact given expert opinion which falls outside his true expertise.

Any expert is entitled to research a topic on which he is to give evidence and obtain the views of others, including work colleagues, about it to enhance his opinion, so long as he records where he went for that advice and so long as it is to enhance an expertise he already has, rather than to become an expert on a subject where he has no knowledge whatsoever.9

The passage highlights the following important matters: 1. It is for the jury to determine, upon hearing the evidence, how much weight to put on an expert’s evidence; 2. Whilst an expert is entitled to update their knowledge of matters on which they are due to give evidence including by approaching third parties, those communications should be logged and reviewed for disclosure. Evidently, and perhaps without needing to be stated, it is clearly undesirable for an expert witness to attempt to become an expert in an area they hold no previous expertise during the course of a trial.

In considering what makes an expert the court went back to 1894 and the case of Silverlock10 and the judgment of Chief Justice Killowen:

” ….It is true that the witness who is called upon to give evidence founded on a comparison of handwritings must be peritus ; he must be skilled in doing so; but we cannot say that he must have become peritus in the way of his business or in any definite way. The question is, is he peritus? Is he skilled? Has he an adequate knowledge? Looking at the matter practically, if a witness is not skilled the judge will tell the jury to disregard his evidence. There is no decision which requires that the evidence of a man who is skilled in comparing handwriting, and who has formed a reliable opinion from past experience, should be excluded because his experience has not been gained in the way of his business……”

An individual can therefore become an expert (or peritus) in a broad range of ways. But ultimately an expert is an expert because they are an expert. As was noted by Bingham LJ in R v Robb11 English law is “characteristically pragmatic”12 in establishing expertise. This benefit of this broad approach to considering expertise allows matters to be assessed on a case by case basis taking into account the particular individual advanced as an expert and the particular issues in the case that are highlighted as requiring expert evidence.

Ultimately the Court of Appeal upheld the convictions in Pabon and others on the basis of the relevance of the expert’s evidence to the ultimate matter in issue – the expert didn’t speak to the issue of dishonesty in respect of the Appellants’ actions.

The independence of experts

Criminal Procedure Rule 19.2 outlines that the expert’s duty lies to the court rather than the party who has instructed them.

Expert’s duty to the court


(1) An expert must help the court to achieve the overriding objective—

(a) by giving opinion which is— (i) objective and unbiased, and (ii) within the expert’s area or areas of expertise; and

(b) by actively assisting the court in fulfilling its duty of case management under rule 3.2, in particular by— (i) complying with directions made by the court, and (ii) at once informing the court of any significant failure (by the expert or another) to take any step required by such a direction.

(2) This duty overrides any obligation to the person from whom the expert receives instructions or by whom the expert is paid.

This overriding duty will often manifest itself in the expert’s report in the form of a declaration confirming that the expert understands their duty is to help the court, by giving assistance by way of objective and unbiased opinion on matters within the experts expertise, and that duty overrides any obligation towards the party by whom they are engaged or paid by.

It is well established that investigating officers can provide expert evidence13. In the conjoined appeals of Myers, Cox and Brangman v R14 in which the Privy Council heard an appeal from the Court of Appeal for Bermuda Hughes SJC noted the following:

But the officer must have made a sufficient study, whether by formal training or through practical experience, to assemble what can properly be regarded as a balanced body of specialised knowledge which would not be available to the tribunal of fact. … But care must be taken that simple, and not necessarily balanced, anecdotal experience is not permitted to assume the robe of expertise. An example is given by the Canadian case Sekhon v The Queen [2014] 1 SCR 272 , where in the course of otherwise perfectly permissible expert evidence as to drug practices, there was adduced from the officer the fact that he had never encountered an innocent courier. That was clearly not a balanced, tested or researched proposition as to the methods of drug importers, but simply his personal experience. It was not admissible and indeed proved nothing about the particular defendant on trial.

Secondly, whilst a police officer may be an expert, by training or experience or both, if he is then he comes under the same duties to the court as does any other expert.15

The court went on to note that compliance with the requirements of an expert may be difficult for a police officer who is combining the duties of an active investigator with providing independent expert evidence. Police witnesses who become expert witnesses should understand they are not part of the prosecution team but have separate independent duties to the court.

Police officers are entitled to give expert evidence on a number of different topics:

Quality of driving – Oakley16 – an office with qualifications and experience in accident investigation can give evidence of how an accident occurred.

Supply of drugs – R v Hodges and Walker17 [2003] – an officer’s evidence was capable of challenge during cross examination and by any evidence to the contrary adduced by the Defence.

Whilst a conflict of evidence does not automatically disqualify the individual from giving expert evidence, where it is material and significant the court is unlikely to grant permission for the evidence to be called. Inevitably, any conflicts of interest must be disclosed so the matter can be addressed by either side.


1R v Bonython [1984] SASR 45

2[2013] EWCA Crim 2

3R v C [2012] EWCA Crim 1478

4R v Terence Turner [1975] QB 834

5R v Abadom [1983] 1 WLR 126

6R v Weller [2010] EWCA Crim 1085 at para 38


8[2018] EWCA Crim 420

9As outlined in R v Pabon [2018] EWCA Crim 420 at para 52

10[1894] 2 QB 766 at 771

11[1991] 93 Cr App R 161

12Ibid at 164

13See R v Oakley [1979] RTR 417 – “we would like to make it quite clear straight away that there is no question of a police officer being prevented from giving evidence as an expert if the subject in which he is giving evidence as an expert is a subject in which he has expert knowledge, and if it is restricted and directed to the issues in the case.”

14[2016] AC 314

15Ibid at para 58-59

16[1979] 70 Cr App R 7

17[2003] EWCA Crim 290