(a) during a vacancy in the office of the member, whether or not an appointment has previously been made to the office; or
(b) during any period, or during all periods, when the member is, for any reason, unable to perform the functions of the office.
(2) A person appointed to act as a member shall not act continuously for more than 12 months.
(3) Anything done in good faith by or in relation to a person purporting to act under subsection (1) is not invalid on the ground that—
(a) the person's appointment was ineffective or had ceased to have effect; or
(b) the occasion for the person to act had not arisen or had ceased.