(1) This rule applies to any proceedings, other than proceedings falling within rule 21.4, in which 5 or more persons have the same or a similar interest.
(2) The court may appoint —
(a) a body having a sufficient interest in the proceedings; or
(b) one or more of those persons, to represent all or some of the persons with the same or similar interest.
(3) A representative under this rule may be either a claimant or a defendant.