27. A person who does not satisfy the all work test shall be treated as incapable of work if in the opinion of a doctor approved by the Department—
(a)he suffers from a previously undiagnosed potentially life-threatening condition;
(b)he suffers from some specific disease or bodily or mental disablement and, by reason of such disease or disablement, there would be a substantial risk to the mental or physical health of any person if he were found capable of work;
(c)he suffers from a severe uncontrolled or uncontrollable disease; or
(d)he will, within 3 months of the date on which the doctor so approved examines him, have a major surgical operation or other major therapeutic procedure.