"A person discriminates against a woman in any circumstances relevant for the purposes of any provision of this Act if - (b) he applies to her a requirement or condition which he applies or would apply equally to a man but - (i) which is such that the proportion of women who can comply with it is considerably smaller than the proportion of men who can comply with it, and
"A comparison of the cases of persons of different sex or marital status under section 1(1) or section 3(1) must be such that the relevant circumstances in the one case are the same, or not materially different, in the other. "
"The choice of an appropriate section of the population is in our judgment an issue of fact (or perhaps strictly a matter for discretion to be exercised in the course of discharging an exclusively fact-finding function) entrusted by Parliament to the good sense of the tribunals, whose selection will be influenced by the need to fit it as closely as possible to the varying circumstances of each case. Of course in those exceptional cases where it can be shown that good sense has not prevailed, and the tribunal has chosen to make the proportionate comparison within an area of society so irrationally inappropriate as to put it outside the range of selection for any reasonable tribunal, then the tribunal would have fallen into an error of law which could be corrected in the appellate jurisdiction."