News Business Crime & Financial Services 13th Jun 2019

“I’m pretty sure I glanced at something”: Due Diligence in Instructing Experts

Gavin Irwin and Amy Woolfson explore the realities of instructing experts under the revised procedure rules

The revised Criminal Practice Rule 19 and Practice Direction V took effect on 1 April 2019.  The new rule places heightened requirements on experts and those instructing them.  Following on from the recent collapse of criminal proceedings at Southwark Crown Court (carbon credit trading) and from the issues raised in the Court of Appeal in the LIBOR appeal, this article places the new requirements in context and suggests practical steps for those instructing experts.


In the early 2000s, a series of miscarriages of justice revealed dangerous shortcomings in the common law rules on expert evidence. In particular, a number of murder convictions based on expert evidence in relation to ‘shaken baby syndrome’ were shown to be unsafe. As part of the response to this, the Law Commission undertook a project on expert evidence in criminal proceedings.

In March 2011, the Law Commission produced their report ‘Expert Evidence in Criminal Proceedings in England and Wales’, accompanied by a draft Bill. The report recommended introducing a statutory test for the admissibility of expert evidence.

In November 2013, the Ministry of Justice confirmed that it did not intend to act on the Law Commission’s recommendations. However, reform of the law has been effected through other means, most notably by way of amendments to the Criminal Procedure Rules (‘CPRs’) and Practice Directions (‘PDs’). The admissibility of expert evidence thus remains subject to common law, supplemented by the CPRs and PDs, and general statutory rules on the admissibility of evidence[1].

The most recent amendments to the CPRs and the PDs were a response to concerns raised by the Forensic Science Regulator about uneven interpretation of the rules by experts.

The New Normal

Crim PR 19.3 now states:

A party who wants to introduce expert evidence otherwise than as admitted fact must—

(a) serve with the report notice of anything of which the party serving it is aware which might reasonably be thought capable of—

i. undermining the reliability of the expert’s opinion, or

ii. detracting from the credibility or impartiality of the expert

Criminal Practice Direction V provides essential guidance on how the rules should be applied. In particular, PD 19B.1 sets out a pro forma statement of understanding and declaration of truth. It is not essential to use the pro forma statement, but any statement should be in substantially similar terms. An expert should make a statement in these terms, or in substantially similar terms as this pro forma statement.

Anything which might reasonably be thought capable of undermining the reliability of the expert’s opinion or detracting from the credibility or impartiality of the expert is a low bar. The Practice Direction further elaborates. PD 19A.7 describes a party not only disclosing material which might reasonably be thought capable of undermining the expert’s opinion, or detracting from the credibility or impartiality of the expert – both in relation to the expert and in relation to any corporation or other body with which the expert works, as an employee or in any other capacity.

PD19A.8 states: In a case in which an expert, or a corporation or body with which the expert works, has been criticised without a full investigation, for example by adverse comment in the course of a judgment, it would be reasonable to expect those criticised to supply information about the conduct and conclusions of any independent investigation into the incident, and to explain what steps, if any, have been taken to address the criticism.

PD19A.9 also states that this should not require disproportionate enquiry. But given the detailed requirements, it is difficult to judge what a proportionate enquiry might be. What if a toxicology expert is a university professor and their department receives funding from a drug company? Or what if someone criticises their research on the basis that ‘they would say that, wouldn’t they – look who funds them’?

Crucially, the CPRs place obligations both on the experts and those instructing them. It is submitted that it is insufficient to accept an expert’s assurances without properly interrogating them. A party who fails to make proper inquiries of an expert they intend to use is running a significant risk. Instructing an expert without sufficient due diligence could cause their evidence may be rejected as inadmissible, or a jury may be invited to place little weight upon it. Aside from the costs implications, it could be devastating for your client – whether you are prosecuting or defending.

What to ask

The pro-forma declaration contained in PD19B.1 is a valuable (and necessary) first step. But as the case of R. v Pabon (Alex Julian) [2018] EWCA Crim 420 (the LIBOR appeal) shows, a signed declaration is not a guarantee of competence. In that case, the prosecution expert had signed the standard-form declaration. During the trial, it became apparent that he was giving evidence outside his area of expertise and did not properly understand his obligations to the court. In response to a direct question regarding the CPRs the expert said ‘I’m pretty sure I glanced at something’. This is clearly not good enough.  Although the conviction was declared safe, the court found that the expert had ‘signally failed to comply with his basic duties’.

Whilst the revised Rules and Practice Direction are more onerous, they do not address the risk of a case like Pabon happening again. It is difficult to see how any standard-form declaration could do. Therefore, those instructing experts are advised to engage in a dialogue with them, rather than accepting written assurances at face value.

The following points are suggestions for best practice when instructing experts. They closely follow the examples in PD 19A.7. These suggestions apply equally to prosecution and defence experts. However, further guidance will apply to the prosecution, for example the CPS Guidance on Expert Evidence.

  1. Speak to your expert – do not rely solely on a pro-forma self-declaration.
  2. Explore what the expert understands their basic duties to be.
  3. Ask the question: “How would you define the limits of their expertise?”
  4. Ask the question: “Are you aware of any criticism levelled at you in any court or tribunal (regardless of the basis of any such criticism)?”
  5. Ask the question: “Are you aware of any criticism levelled at you in peer-reviewed journals / specialist media (regardless of the basis of any such criticism)?”
  6. Ask the question: “Are you regulated by any professional body?”
  7. If not, ask the question: “If you have chosen not to be registered with a representative professional body, why not?”
  8. Ask the question: “Are you now, or have you ever been, or, to the best of your knowledge, are you likely soon to be, subject to any regulatory action?”
  9. Search a database of higher court judgments by reference to the expert’s name.
  10. Consider any relevant judgments for expressions of criticism.

When to ask

These questions should be asked every time an expert is instructed.  That is, before instruction, during the process of selecting the best / most appropriate expert.  You should not assume that because a person is an established expert witness that they will pass the tests.  The expert in Pabon was a regular prosecution expert for the SFO. Where you are instructing the same expert on a regular basis, it will be necessary to review their expertise as it relates to the instant case and, periodically, to ensure that the answers to the questions above have not changed.


  1. The direction of travel is clear: experts should expect greater scrutiny; and, those who instruct them need to be ready for what enhanced due diligence might reveal.
  2. More change is expected soon: in the related field of forensic science, the House of Lords Science and Technology Committee Report of 1 May 2019[2], has called for the Forensic Science Regulator to be placed on a statutory footing and for the process of accreditation to be overhauled.

In the meantime, it is hoped that this article will provide some assistance.

[1] See Poilce and Criminal Evidence Act 1984, and, Criminal Procedure and Investigations Act 1996, as amended.


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