What is the test for imputed knowledge of a partner in a law firm?

It is on issue of "imputed knowledge" that the minority in Martin v. Gray parted company from the majority. Cory J., writing for the minority, was of the view that the presumption that disclosure between the "tainted" member and the other members of the firm has or will occur should be an irrebuttable one. He concluded, at pages 271-272: He [Sopinka J.] states that the position, taken by some courts, that if one lawyer in the firm cannot act, then no member of the law firm can act, is unreasonable in this era of mega-firms and mergers. Thus, he reasons that it should be open for a solicitor to show "that no information was imparted which could be relevant." With respect, I disagree. Neither the merger of law firms nor the mobility of lawyers can be permitted to adversely affect the public's confidence in the judicial system. At this time, when the work of the courts is having a very significant impact upon the lives and affairs of all Canadians, it is fundamentally important that justice not only be done, but appear to be done in the eyes of the public. ..... ..... In preparing for the hearing of a contentious matter, a client will often be required to reveal to the lawyer retained highly confidential information. The client's most secret devices and desires, the client's most frightening fears will often, of necessity, be revealed. The client must be secure in the knowledge that the lawyer will neither disclose nor take advantage of these revelations. Our judicial system could not operate if this were not the case. It cannot function properly if doubt or suspicion exists in the mind of the public that the confidential information disclosed by a client to a lawyer might be revealed. ..... Fortunately, partners rarely attempt to act for clients on both sides of a lawsuit. However, the problem more frequently arises when a lawyer, who has received confidential information, joins a firm that is acting for those opposing the interests of the former client. In such a situation there should be an irrebuttable presumption that lawyers who work together share each other's confidences with the result that knowledge of confidential matters is imputed to other members of the firm. This presumption must apply to the members of the new firm the lawyer joins if public confidence in the administration of justice is to be maintained. (emphasis added)