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.