“The term ‘acquiescence’ is, however, properly used where a person having a right, and seeing another person about to commit, or in the course of committing, an act infringing that right, stands by in such a manner as really to induce the person committing the act, and who might otherwise have abstained from it, to believe that he assents to its being committed; a person so standing by cannot afterwards be heard to complain of the act. In that sense the doctrine of acquiescence may be defined as quiescence under such circumstances that assent may be reasonably inferred from it, and is no more than an instance of the law of estoppel by words or conduct, the principle of estoppel by representation applying both at law and in equity, although its application to acquiescence is equitable. The estoppel rests upon the circumstances that the person standing by in effect makes a misrepresentation as to a fact, namely, his own title; a mere statement that he intends to do something, for example to abandon his right, is not enough. Furthermore, equitable estoppel is not applied in favour of a volunteer.”
“Furthermore the more recent cases indicate, in my judgment, that the application of the Ramsden v Dyson L.R. 1 H.L.129 principle – whether you call it proprietary estoppel, estoppel by acquiescence or estoppel by encouragement is really immaterial – requires a very much broader approach which is directed rather at ascertaining whether, in particular individual circumstances, it would be unconscionable for a party to be permitted to deny that which, knowingly, or unknowingly, he has allowed or encouraged another to assume to his detriment than to enquiring whether the circumstances can be fitted within the confines of some preconceived formula serving as a universal yardstick for every form of unconscionable behaviour.”
“Nevertheless, while falling short of estoppel, in my judgment the behaviour of the Plaintiffs, coupled with the very long delay, really amounted to an acknowledgement by them of the Defendants’ right to continue the use of their (the Defendants’) marks, and to a waiver of the Plaintiff’s right to sue for infringement by such continued user. I accept the Defendants’ submission that really the course of conduct between the parties showed a mutual policy of restraint to one another, or, putting it more colloquially, a mutual agreement to live and let live.”