What is the effect of the words "if and so far as a contrary intention in not expressed" under s. 80 of the Law of Property Act, 1925?

A similar conclusion was expressed by Lord Russell of Killowen in Kirk v. Eustace, [1937] A.C. 491 (H.L. (E.) ) in which the words "if and so far as a contrary intention in not expressed" found in s. 80 of the Law of Property Act, 1925, were considered. He said (at p. 498) : Mere implication of such an intention, even if any grounds for such an implication existed in the present case (and in my opinion no such grounds exist), would be insufficient.

In Re Jones's Will Trusts; Jones v. Hawtin Squire, [1965] 1 Ch. 1124, Buckley J. noted that s. 16 of the Adoption Act, 1958, "does not say in terms that the contrary intention must appear on the face of the instrument", but concluded (at p. 1131) : ... in the absence of any such qualification, I think that the words "unless the contrary [intention] appears," means unless the contrary appears from any surrounding circumstances which carry conviction to the mind of the court. (My emphasis.)