Estoppel

Under established case law, the principles applicable to the assertion of an estoppel by convention arising out of non-contractual dealings were:

(i) it was not enough that the common assumption upon which the estoppel was based was merely understood by the parties in the same way. It had to be expressly shared between them;
(ii) the expression of the common assumption by the party alleged to be estopped had to be such that he might properly be said to have assumed some element of responsibility for it, in the sense of conveying to the other party an understanding that he expected the other party to rely upon it;
(iii) the person alleging the estoppel had to, in fact, have relied upon the common assumption, to a sufficient extent, rather than merely upon his own independent view of the matter;
(iv) that reliance had to have occurred in connection with some subsequent mutual dealing between the parties; and
(v) some detriment