If, at any stage of the inquiry, the Commission—
         (a) considers it necessary to inquire into the conduct of any person; or
         (b) is of the opinion that the reputation of any person is likely to be prejudicially affected by the inquiry,
it shall give to that person a reasonable opportunity of being heard in the inquiry and to produce evidence in his defence:
Provided that nothing in this section shall apply where the credit of a witness is being impeached.