"The proceeding, then, raises a short but surprisingly difficult point: whether, by asserting that it acted in reliance upon a matter, a party to litigation is putting in issue its state of mind in so acting, so as to waive legal professional privilege with respect to legal communications which might have had a bearing on its arriving at that state of mind. I start from the proposition that legal professional privilege is an important common law immunity which is not lightly to be abrogated. Where it applies, the privilege has the consequence that information material to litigation is denied to the opposing party and to the Court. The privilege, therefore, competes with the policy which demands that all relevant evidence be available to the Court. While the formulation of the privilege rule might itself represent an attempt to balance these competing interests, the application of the rule does not; to adopt the striking image of Heerey J in Equuscorp Pty Ltd v Kamisha Corporation Ltd, 'If legal professional privilege applies, privilege trumps relevance'. It follows from this that mere materiality to an issue in litigation can provide no ground to remove the privilege. There must be more. Otherwise, the privilege would have no work to do, for materiality is a fundamental precondition to the admissibility of any piece of evidence. The privilege, however, is an immunity which belongs to the client and may be waived by the client. Waiver may be express or implied or imputed in a variety of situations and this may occur prior to the commencement of a proceeding, during its interlocutory stages or at trial. I am here concerned with the case where the suggested waiver arises because Liquorland, the client, has in its pleading put in issue the privileged communication. It has therefore been characterised as 'issue waiver', as opposed to disclosure waiver. I am, moreover, concerned only with the pleading of Liquorland, not with those of the defendants except in the sense that the process of discovery depends upon the existence of an issue raised by the responding plea of the defendants." (Citations omitted)