19(1)If—U.K.
(a)an instrument framed in a form prescribed as mentioned in paragraph 2(2) creates a power which is not a valid enduring power, and
(b)the power is revoked by the mental incapacity of the donor,
sub-paragraphs (2) and (3) apply, whether or not the instrument has been registered.
(2)An attorney who acts in pursuance of the power does not, by reason of the revocation, incur any liability (either to the donor or to any other person) unless at the time of acting he knows—
(a)that the instrument did not create a valid enduring power, and
(b)that the donor has become mentally incapable.
(3)Any transaction between the attorney and another person is, in favour of that person, as valid as if the power had then been in existence, unless at the time of the transaction that person knows—
(a)that the instrument did not create a valid enduring power, and
(b)that the donor has become mentally incapable.
(4)Paragraph 18(4) applies for the purpose of determining whether a transaction was valid by virtue of sub-paragraph (3) as it applies for the purpose or determining whether a transaction was valid by virtue of paragraph 18(3).