What is the leading authority in the examination of conflict of interest involving solicitor and client?

The leading authority in the area of an examination of conflict of interest involving solicitor and client is found in MacDonald Estate v. Martin, 1990 CanLII 32 (SCC), [1991] 1 W.W.R. 705 (S.C.C.).

In MacDonald Estate v. Martin the plaintiff brought an action against the defendant for an accounting. The defendant's solicitor was assisted by a junior member of the firm, who was actively engaged in the file and who was privy to many confidences disclosed by the defendant. Some years later the junior joined the firm which represented the plaintiff. The plaintiff had been represented by the same firm for some years, and as the matter neared trial was reluctant to change solicitors. Affidavits were sworn that the case had not been and would not be discussed with the junior. The junior also swore that she had not betrayed and would not betray confidences. The defendant obtained an order declaring the plaintiff's firm ineligible to continue to act as solicitors of record for the plaintiff and removing the firm as solicitors of record. The decision was reversed on appeal. The defendant appealed further. The sole issue was the appropriate standard to be applied in determining whether the plaintiff's firm was disqualified from continuing to act in the case by reason of conflict of interest.