Expert witnesses in English law
The role of expert witnesses in English law is to give explanations of difficult or technical topics in civil and criminal trials, to assist the fact finding process.
The extent to which authorities have been allowed to testify, and on what topics, has been debated, and to this end a variety of criteria have evolved throughout English case law.
To this end they represent an exception to the general rule against opinion,[2] because to follow such a strict approach otherwise would result in much scientific or technical evidence being disregarded when it was not understood.
However, as fields of scientific knowledge continue to expand, and with the advent of forensic evidence, such instances are now commonplace, and the need for experts has been described as "ever-expanding".
The Criminal Procedure (Insanity and Unfitness to Plead) Act 1991 requires: written or oral evidence of two or more registered medical practitioners at least one of whom is duly approved.Where an individual attempts to adduce expert evidence in aid of their defence, they must have been suffering from a genuine and recognised mental condition, which was capable of producing effects on the mind and body outside the expertise of the tribunal.
It has been made clear that in cases where individuals are merely vulnerable or easily susceptible to suggestion, expert witnesses may not be called in order to testify to such characteristics.
"[7]This case has been followed by R v Walker,[8] where an individual accused of shoplifting attempted to adduce expert evidence of their condition, which it was claimed made them more vulnerable to threats of duress.
While the case was described as borderline by the Court of Appeal, it was decided that such evidence could be properly admitted where it was not commonly found in ordinary individuals.
The test as to where this will be permissible is similar to that used for general psychiatric evidence; the individual seeking to adduce expert testimony must have been suffering from a genuine personality disorder outside the understanding of the tribunal, and this must have some effect of rendering their confession unreliable.
In R v Blackburn[20] the Court of Appeal ruled that the area of coerced confessions fell outside the experience of ordinary individuals, and thus expert evidence may be adduced where this is at issue.
[1]: 536 Without having regard to these factors, the Court of Appeal decided controversially that ear-print identifications were admissible, despite a general consensus as to their ability to identify individuals uniquely.
The same principles were approved in R v Luttrell,[24] where the Court established that in some occasions, the reliability of expert evidence would not affect its admissibility, but merely require a warning as to its shortcomings and error rate in the form of jury instructions.
Decisions regarding helpfulness of evidence often depends upon the facts of the case and are made by the judge and tend to be contextual rather than based on fixed legal principles.
