13In section 31(3) for the words from "but" to "presumed" there shall be substituted the words " a person is of unsound mind if he is a person who, by reason of mental disorder within the meaning of the Mental Health Act 1959, is incapable of managing and administering his property and affairs ; and, without prejudice to the generality of the foregoing provision, a person shall be conclusively presumed for the purposes of that subsection ".