Nothing in this Part renders unlawful discrimination on the ground of sex in the terms or conditions appertaining to a superannuation or provident fund or scheme, where--
(a) the terms or conditions--(i) are based upon actuarial or statistical data on which it is reasonable to rely, and(ii) are reasonable having regard to the data and any other relevant factors, or
(b) in a case where no such actuarial or statistical data is available and cannot reasonably be obtained--the terms or conditions are reasonable having regard to any other relevant factors,and the source on which any data referred to in paragraph (a) is based is disclosed to the Tribunal, where the Tribunal so requires, and any other relevant factors to which regard has been had as referred to in paragraph (a) or (b) are disclosed to the Tribunal, where the Tribunal so requires.