What is the legal test for disclosing privileged information?

I will read a passage from Martin v. Gray that talks about the questions to be answered in addressing that. I do not have the paragraph number. Typically, these cases require two questions to be answered. 1. Did the lawyer receive confidential information attributable to a solicitor-and-client relationship relevant to the matter at hand? 2. Is there a risk that it will be used to the prejudice of the client? In answering the first question, the court is confronted with a dilemma. In order to explore the matter in depth may require the very confidential information for which protection is sought to be revealed. This would have the effect of defeating the whole purpose of the application. American courts have solved this dilemma by means of the "substantial relationship" test. Once a “substantial relationship" is shown, there is an "irrebuttable presumption” that confidential information was imparted to the lawyer. In my opinion, this test is too rigid. There may be cases in which it is established beyond any reasonable doubt that no confidential information relevant to the current matter was disclosed. One example is where the applicant client admits on cross-examination that this is the case. This would not avail in the face of an irrebuttable presumption. In my opinion, once it is shown by the client that there existed a previous relationship, which is sufficiently related to the retainer from which it is sought to remove the solicitor, the court should infer that confidential information was imparted, unless the solicitor has satisfied the court that no information was imparted which could be relevant. This will be a difficult burden to discharge. Not only must the court's degree of satisfaction be such that it would withstand the scrutiny of the reasonably informed member of the public that no such information passed, but the burden must be discharged without revealing the specifics of the privileged communication. None the less, I am of the opinion that the door should not be shut completely on a solicitor who wishes to discharge this heavy burden. The second question is whether the confidential information will be misused. A lawyer who has relevant confidential information cannot act against his client or former client. In such a case, the disqualification is automatic. No assurances or undertakings not to use the information will avail. The lawyer cannot compartmentalize his or her mind so as to screen out what has been gleaned from the client and what was acquired elsewhere. Furthermore, there would be a danger that the lawyer would avoid use of information acquired legitimately because it might be perceived to have come from the client. This would prevent the lawyer from adequately representing the new client. Moreover, the former client would feel at a disadvantage. Questions put in cross-examination about personal matters, for example, would create the uneasy feeling that they had their genesis in the previous relationship.