(1) For the purpose of any provision of this Act or any other Act under which a power in respect of the investigation of offences or the treatment of persons in police custody is exercisable only by or with the authority of a police officer of at least the rank of superintendent, an officer of the rank of chief inspector shall be treated as holding the rank of superintendent if
(a) he has been authorised by an officer holding a rank above the rank of superintendent to exercise the power or, as the case may be, to give his authority for its exercise, or
(b) he is acting during the absence of an officer holding the rank of superintendent who has authorised him, for the duration of that absence, to exercise the power or, as the case may be, to give his authority for its exercise.
(2) For the purpose of any provision of this Act or any other Act under which such a power is exercisable only by or with the authority of an officer of at least the rank of inspector, an officer of the rank of sergeant shall be treated as holding the rank of inspector if he has been authorised by an officer of at least the rank of superintendent to exercise the power or, as the case may be, to give his authority for its exercise.