In Re Bateman’s Will Trusts [1970] 1 WLR 1463, the testator’s will stated that income was to be paid ‘to such persons and in such proportions as shall be stated by me in a sealed letter . . . addressed to my trustees’. The court held that the trust was invalid. Pennycuick V-C said that the words:

…import that the testator may, in the future, after the date of the will, give a sealed envelope to his trustees. It is impossible to confine the words to a sealed letter already so given. If that is the true construction of the wording, it is not in dispute that the direction is invalid . . . as an attempt to dispose of the estate by a non-testamentary instrument.

It would seem from this that, whenever the trust is communicated, it will fail if the will allows for future communication.