Sir Adolph Tuck, a baronet who had run the art publisher Raphael Tuck & Sons, created a trust for future baronets who were married to a wife 'of Jewish blood' and who 'continues to worship according to the Jewish faith'.

If in doubt, 'the decision of the Chief Rabbi in London of either the Portuguese or Anglo German Community… shall be conclusive'.

Lord Denning MR held the trust was valid, and the Chief Rabbi could resolve any uncertainty.

If this argument is correct, it means that the intentions of the settlor, Sir Adolph, have been completely defeated by the ingenuity of the lawyers: first, in discovering the uncertainty: and, secondly, in refusing to allow it to be cured by reference to the Chief Rabbi.

"Conceptual uncertainty" arises where a testator or settlor makes a bequest or gift upon a condition in which he has not expressed himself clearly enough.

"Evidential uncertainty" arises where the testator or settlor, in making the condition, has expressed himself clearly enough.

It has to resort to extrinsic evidence to discover the facts, for instance to ascertain those whom the testator or settlor intended to benefit and those whom he did not.

This dichotomy between "conceptual" and "evidential" uncertainty was adumbrated by Jenkins J. in Re Coxen (1948) Chancery at pages 761/2.

The reason in each case being that the testator had given no information or clue as to what percentage or proportion of Jewish blood would satisfy the requirement.

I do not so find it.Eveleigh LJ said the trust was valid, but only because the Chief Rabbi’s opinion of who was Jewish was part of the definition of the class of beneficiaries.