The expert

Specialist inspectors

Specialist inspectors might be involved in an investigation either as part of the investigation team (albeit with specialist knowledge) or as an independent expert witness. The specialist knowledge of inspectors involved in an investigation may allow them to be treated as an expert witness in the event of a prosecution. It has been held by the Court of Appeal in a civil case that the fact that an expert may be the employee of one of the parties to litigation would not debar him/her from giving expert evidence. The same principle applies to inspectors acting as experts in HSE prosecutions.

However, the roles of investigator and expert witness may be mutually exclusive, and a specialist inspector may not be asked to act as expert if s/he is directly involved in the investigation. The decision as to whether an 'independent expert' is required, and who it should be, rests with the procurator fiscal.

Whilst a specialist inspector may advise the investigator(s) on the gathering of evidence, such as questions to put to witnesses or to a suspect, if a specialist has been appointed (or is intending) to act as a potential expert, s/he should remain independent of the investigation and should be seen to do so: s/he should generally not take statements as part of the investigation or attend an interview of a suspect under caution - see Operational Procedures. If a specialist inspector (who is not to act as an expert) attends an interview under caution the fact of their specialist expertise should be disclosed.

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The role of an expert

Expert witnesses enjoy three privileges over ordinary witnesses of fact:

  • With the courts permission they may remain in court prior to giving evidence, subject to argument about disputed factual evidence they may give, in order to hear evidence of both fact and circumstance.
  • They may express an opinion on matters within their field of expertise; and
  • They may refer to the works of others within their field of expertise without infringing the rules against hearsay - see the Hearsay section.

An expert witness may give opinions to assist in resolving issues concerning matters of knowledge which can only be acquired by special training or experience. His/her role is to assist the court or jury on matters where their ordinary, everyday experience does not enable them to adequately consider the issues in the case.

The facts on which the expert's opinions are based must be either admitted or proved by admissible evidence. Usually, such facts are established by other witnesses but they may include facts observed by the expert him/herself.

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Duties of an expert

An expert's opinion must be objective and unbiased. Although a defendant will be entitled to call their own expert evidence, it is the duty of an expert witness instructed by the prosecution (and indeed an expert witness called by any defendant) in a criminal case to act in the cause of justice. An expert's duty to the court overrides any obligation to the party instructing him/her and s/he should maintain professional objectivity and impartiality at all times whilst complying with the rules of evidence.

The responsibilities in relation to expert evidence are shared between the expert and the prosecutor, but it is the prosecutor who has overall responsibility for the case; the expert is expected to assist with that task.

The duties and responsibilities of expert witnesses in criminal cases have been summarised and include the following:

  • Expert evidence presented to the court should be (and be seen to be) the independent product of the expert and should not be influenced as to form or content by the demands of litigation;
  • An expert witness should provide independent assistance to the court in relation to matters within his or her expertise. An expert witness should never assume the role of an advocate;
  • An expert witness should state the facts or assumptions upon which his/her opinion is based. S/he should consider all material facts in drawing conclusions and should not omit to consider those that detract from his/her conclusions;
  • An expert witness should make it clear when a particular question or issue falls outside his/her expertise. The opinion of an expert is only admissible if s/he is competent (ie qualified), through study, training or experience, in a field relevant to the case;
  • If an expert considers that insufficient data is available to allow him/her to come to a final conclusion, this must be stated with an indication that the opinion is a provisional one;
  • If, after exchange of reports, an expert witness changes his/her view on a material matter (having read the defence expert's report or for any other reason), such change of view should be communicated to the procurator fiscal without delay;
  • Experts who are civil servants must also carry out their duties in accordance with the Civil Service Code and its core values of integrity, honesty, objectivity and impartiality. The Code reinforces the standards expected of all experts by the courts.

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Instructing an expert

It is the responsibility of the person managing the investigation to manage the use of specialists, deciding how they should be used and ensuring that experts remain independent.

Any correspondence with an expert pertaining to his/her instructions may be disclosable and the defence will be entitled to see it. Whilst instructions to an expert explaining what is being asked of him/her will normally be recorded in formal correspondence (and see also the section 'The report'), the defence may also be entitled to see any "informal" correspondence.

When an expert witness is instructed, it is important that they understand what is required of him/her. They should be referred to this section of the Enforcement Guide and also the section on disclosure mentioned above. The expert must fully understand that s/he has an overriding duty to assist the court and should not feel prevented from providing information that might prove detrimental to the prosecution case. In order to meet that overriding duty, s/he is under an obligation to assist the prosecution with the statutory requirements relating to disclosure. The expert should be reminded of this obligation, which takes precedence over any internal codes of practice or other standards set by professional organisations.

Those instructing an expert will need to think carefully about what information should be supplied to him/her. An expert enjoys particular privileges arising from his/her qualifications and expertise. Those privileges, in particular the ability to put opinion evidence before the jury, can be undermined if it appears that his/her opinion has been improperly influenced. Any material provided to the expert should be listed in the original and any subsequent instructions. The expert should not be given material (such as internal prosecution or investigation reports) which is likely to contain opinion evidence from people other than witnesses of fact or other experts. The defence is entitled to see all material provided to the expert by those instructing him/her and therefore sensitive or privileged material must not be supplied.

Experts should not be asked to conduct tests that will only favour the prosecution. Investigators should pursue all reasonable lines of enquiry, and this means that tests that might undermine the prosecution case should also be commissioned.

Responsibility for directing the investigation remains with those instructing the expert. If the expert believes that further work or information is required, or if s/he changes his/her evidence, s/he should communicate this to the person managing the investigation. Discussions with experts should be recorded, as they are clearly relevant to the investigation (and disclosable), particularly any discussion in which additional information is provided to the expert.

Experts should be reminded that a failure to comply with their duties could have a number of adverse consequences, including the delay or halting of the prosecution case, the overturning of any conviction and criticism of the expert by the judge, which might result in referral of the expert to any relevant professional body. Such consequences might prevent him/her from acting as an expert in future.

If questions remain about the role or instruction of experts, advice should be sought via your legal liaison point.

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Updated 2020-11-16