A vehicle engineer who has spent years writing civil reports can be caught out the first time a defence solicitor, or the Crown, instructs them in a prosecution for dangerous or careless driving. The physics is the same. The procedural setting is not, and the differences are not cosmetic.
The same duty, more sharply drawn
Rule 19.2 of the Criminal Procedure Rules states the expert’s duty in terms that echo CPR Part 35: to help the court to achieve the overriding objective by giving opinion which is objective and unbiased, and within the expert’s area of expertise. The duty overrides any obligation to the person instructing or paying. So far, familiar.
Rule 19.2 then adds something civil practitioners will not have met. The expert must help the court by complying with directions, by informing the parties and the court of any significant failure to take a step required by a direction, and, under rule 19.2(3)(d), by disclosing to the party instructing them anything of which the expert is aware that might reasonably be thought capable of undermining the reliability of the expert’s opinion, or detracting from the expert’s credibility or impartiality. The instructing party must in turn serve that information with the report under rule 19.3. In other words, the criminal rules oblige the expert to volunteer their own weaknesses.
For an engineer that means more than declaring a conflict of interest. It includes the limits of the method used, data that points the other way, prior occasions on which the expert’s evidence was criticised, and any respect in which the instructed question sits at the edge of their competence. Writing those things down is uncomfortable the first time and routine thereafter. A report that does it well is hard to attack precisely because it has already said what the attack would be.
The contents of the report
Rule 19.4 lists what a criminal expert report must contain, and the list closely parallels Practice Direction 35: qualifications, relevant experience and accreditation; the literature and other material relied on; the substance of all facts given to the expert which are material to the opinion; which facts are within the expert’s own knowledge; who carried out any examination, measurement, test or experiment, their qualifications and whether it was under supervision; the range of opinion where one exists and the reasons for the expert’s own; a summary of conclusions; any qualification on the opinion; and the declaration that the expert understands and has complied with the duty to the court. The Criminal Practice Directions prescribe the wording of that declaration, which is longer and more specific than its civil counterpart, and it should be reproduced exactly.
Reliability
The Law Commission recommended in 2011 that there be a statutory test of reliability for expert evidence in criminal trials. Parliament did not legislate, but the substance of the recommendation found its way into the Criminal Practice Directions. The current Directions set out the factors a court may take into account in deciding whether expert opinion is sufficiently reliable to be admitted: among them, the extent and quality of the data on which the opinion is based and the validity of the methods used; whether the opinion properly explains how safe or unsafe it is, by reference to error rates, confidence intervals or otherwise; whether the opinion takes proper account of matters that might detract from it; the completeness of the information available to the expert; and whether the expert’s methods followed established practice in the field, and if not, why not.
Read as an engineer, that is a specification. A collision analysis that gives a speed as a range, explains the inputs that drive the width of the range, cites the source of each coefficient and says what evidence was unavailable is answering the reliability test in the order the Directions ask it.
The offences and what the engineer is actually asked
In driving prosecutions under the Road Traffic Act 1988, the questions put to an engineer are usually narrow: speed before braking, the timings that recorded data and video fix, whether a vehicle defect contributed, and whether the data from the vehicle or a camera supports or contradicts an account. Questions about what a driver could have seen or done in the time available belong to a collision investigator or a human-factors expert, and an engineer should say so. The standard the court applies to the driving, whether it fell far below, or below, what would be expected of a competent and careful driver, is a question for the tribunal of fact, not for the expert. R v Turner remains the touchstone: expert evidence is admissible to furnish the court with information likely to be outside its own knowledge and experience, and not otherwise. An engineer who strays from “the vehicle was travelling between 46 and 52 mph” into “the driving was dangerous” has stepped outside their role and invited the court to discount the rest.
Pre-hearing discussions and the trial
Rule 19.6 allows the court to direct the experts to discuss the issues and prepare a statement of what is agreed and what is not, with reasons. The Court of Appeal in R v Harris emphasised that experts should engage with that process properly and that a joint statement which narrows the issues is of real value. At trial, the expert’s evidence is given to a jury in the Crown Court or to magistrates, and the test of a good report is whether a non-specialist can follow each step from the evidence to the conclusion. Diagrams, a short glossary and a clear separation of fact, assumption and opinion matter more here than anywhere.
Funding
Where the defendant is legally aided, the expert’s fee and any attendance at court must be authorised in advance by the Legal Aid Agency. The quotation needs to be in the form that process requires, with the hours, the rate basis and the attendance costed together so that a single application covers the work. An engineer who understands that saves the instructing solicitor time and avoids the report being delayed by a second application.