(1) A difference of treatment which is based on a characteristic related to the gender ground in respect of access to employment in a particular post shall not constitute discrimination under this Part or Part II where, by reason of the particular occupational activities concerned or of the context in which they are carried out -

(a) the characteristic constitutes a genuine and determining occupational requirement for the post, and

(b) the objective is legitimate and the requirement proportionate.

(2) In subsection (1) the reference to employment includes a reference to any training leading to it.