How have privies been interpreted in the context of issue estoppel?

147 The concept of privies has been the subject of considerable judicial comment. It becomes relevant when, as in this case, issue estoppel may be a reason for declaring an action to be res judicata. The subject was fully discussed and the authorities reviewed by Dickson J. (as he then was) in Angle v. M.N.R., 1974 CanLII 168 (SCC), [1975] 2 S.C.R. 248. There he quoted from Lord Guest who defined the requirements of issue estoppel at p. 254 as: … (1) that the same question has been decided; (2) that the judicial decision which is said to create the estoppel was final; and, (3) that the parties to the judicial decision or their privies were the same persons as the parties to the proceedings in which the estoppel is raised or their privies …..