Under what circumstances a legally unqualified person can appear on behalf of another person in legal proceedings, broken down by criminal …

In terms of both the civil and criminal courts, the only persons who are generally permitted to appear and conduct cases are members of the Faculty of Advocates, solicitor advocates or solicitors and parties who are natural persons (party litigants). In general solicitors are only able to appear before the district court and the sheriff court, except for solicitor advocates who have acquired rights of audience in the supreme courts. There are some exceptions. As regards civil proceedings:In respect of small claims actions an authorised lay representative may in representing a party do everything for the preparation and conduct of a small claim as may be done by an individual conducting his own claim. (Sheriff Courts (Scotland) Act 1971, section 36 and related rules of court).
Section 97 of the Debtors (Scotland) Act 1987 and related rules of court entitles a party to any proceedings under the act to be represented by a person other than an advocate or a solicitor, if the sheriff is satisfied that such a person is a suitable representative and is duly authorised to represent the party.
As regards criminal proceedings:At the first diet in summary proceedings where the accused is not present, a person (who is not an advocate or solicitor) who satisfies the court that he is authorised by the accused may tender a plea of guilty or not guilty on behalf of the accused (section 144(2)(b) of the Criminal Procedure (Scotland) Act 1995)
In addition, under section 4(2) of the Fatal Accidents and Sudden Deaths Inquiry (Scotland) Act 1976 any person entitled to appear at an inquiry may appear on his own behalf or be represented by an advocate or a solicitor or, with the leave of the sheriff by any other person.