For the purpose of any provision of this Act relating to sickness or invalidity benefit a day shall not be treated in relation to any person as a day of incapacity for work—
(a) unless on that day he or she is deemed, in accordance with the regulations, to be incapable of work by reason of some specific disease or bodily or mental disablement; or
(b) where in the normal course of his or her employment (which has not been terminated) he or she would not work on that day.