In our recent briefing, "Litigation Update - New Rules to Improve Litigation and Cut Delay",1 we explained that new rules of court, which have since taken effect in part from October 2016, give the High Court power, among other things, to exclude expert evidence where the court considers that evidence is not "reasonably required to enable the court to determine the proceedings".2 Now, in a recent judgement,3 the High Court has considered how that rule will apply.

The plaintiff 's principal claim was for orders against a parliamentary Committee on Procedure and Privileges to whom the plaintiff had complained about the publication by members under parliamentary privilege of private information concerning his personal banking arrangements which were already the subject of litigation. As the case raised complex privacy law issues, he sought to be permitted to adduce evidence of a well-known American constitutional law expert. The defendants argued that the proposed evidence should not be admitted in evidence.

The court decided the application principally on the basis that the plaintiff 's claim asserted rights under the Irish law, deriving principally from the Irish Constitution, common law and statute law. It held that while the court would be required to make determinations on Irish law, it was well-established that expert evidence is not admissible in respect of a matter of domestic law. If a question of foreign law falls to be decided, the court can and will receive expert evidence from foreign lawyers on the topic, and if they disagree, the court has to decide what the foreign law is as a matter of fact.4 While there was no doubt as to the expert's eminence in American constitutional law, no issue of American law in fact fell to be decided in the proceedings and accordingly his evidence was inadmissible, though it remained open to the parties to cite decisions of the courts of other states, including the United States courts, for consideration as persuasive authorities.

While that conclusion decided the application, the court took the opportunity, as this was the first time that the new rule on experts had been raised, to comment on it.

The court said:

"This rule gives a measure of badly needed statutory control to the Court in respect of expert evidence. The various decisions in recent years where judges both at trial and at appellate level have commented adversely on the number, extent and costs of experts, demonstrates this need. Under this rule the court is entitled to restrict such evidence to that which is reasonably required to enable the court to determine the proceedings. No longer are parties free to call expert witnesses willy nilly. The court can determine what is needed and restrict expert testimony accordingly.

Having regard to the issues which will fall to be decided in this case I cannot see how the proposed evidence ... could be said to be required at all, still less reasonably required, to enable the court to determine the plaintiff 's claim.

As there is no reasonable requirement for this evidence it follows that even if it were to be regarded as admissible it should, nonetheless, be disallowed."

Although the new rule was not strictly engaged, this judgment reflects a clear statement of intent on the part of the Irish courts to exclude on an ex ante basis expert evidence proffered in litigation which the court does not consider necessary to determine the real issues in dispute. While parties to litigation will very often benefit from the input of a relevant expert who might not ultimately be called as a witness, they should in future consider very carefully whether any expert evidence they might consider calling will pass the "reasonable necessity" test.