4. The period prescribed for the purpose of subsections (4)(a) and (6)(a) of section 7B (power of the tribunal to draw inferences from an employer’s failure to reply to a question within such period) shall be—
(a)except where sub-paragraph (b) applies, the period of eight weeks starting on the day that a question was duly served; or
(b)where a question was asked before 6th April 2003, the period of eight weeks starting on 6th April 2003.