(1) A donee of a power of attorney who acts in pursuance of the power at a time when it has been revoked shall not, by reason of the revocation, incur any liability (either to the donor or to any other person) if at that time the donee did not know that the power had been revoked.

(2) Where a power of attorney has been revoked and a person, without knowledge of the revocation, deals with the donee of the power, the transaction between them shall, in favour of that person, be as valid as if the power had then been in force.

(3) Where the power is expressed in the instrument creating it to be irrevocable and to be given by way of security then, unless the person dealing with the donee knows that it was not in fact given by way of security, that person shall be entitled to assume that the power is incapable of revocation except by the donor acting with the consent of the donee and shall accordingly be treated for the purposes of subsection (2) as having knowledge of the revocation only if that person knows that it has been revoked in that manner.