It has been argued strenuously that upon a matter which involves a question of law no person who is not a professional lawyer could be regarded as a competent expert. Their Lordships do not agree. In the case of Vander Donckt v. Thellusson (1849) 8 C.B. 812 at p. 814 it was held that a person who though not a lawyer, had become conversant with a point of foreign law by “carrying on a business which made it his interest to take cognizance” of the point, was a competent witness on that point. Their Lordships share this view. A number of other cases were cited to their which, although they contain observations relevant to the facts of each case do not, in their Lordships view, qualify in any way the principle stated in their Lordships’ view Lordships do not propose to refer to each of these cases separately. A principle which emerges from them considered together is that not only the general nature, but also the precise character of the question upon which expert evidence is required, have to be taken into account when deciding whether the qualifications of a person entitle him to be regard as a competent expert. So the practical knowledge of a person who is not a lawyer may be sufficient in certain case to qualify him as a competent expert on a question of foreign law … The knowledge which entitles a person to be deemed “specially skilled” on some points foreign law may in their Lordships opinion be gained in appropriate circumstances by a person whose profession is not that of the law. Secondly that he did in fact take cognizance of what notes were legal tender in that country.
— Verity, C. Ajami v. Comptroller of Customs (1952) 14 WACA 34