(1) If, at any time

(a) during the last 4 weeks of subsection (1)(a) leave, or, as the case may be, subsection (1A) leave, whether or not such leave or part of it is postponed under section 16B and where, in accordance with section 16(6), a father or other parent has, or is deemed under section 16B(2) to have, notified his employer, or caused his employer to be notified, of his intention to take further leave under section 16(4), or

(b) during subsection (1)(b) leave or a period of further leave under section 16(4), whether or not such leave or a part of it is postponed under section 16B,

a father or other parent who is sick wishes to terminate his subsection (1)(b) leave or a period of further leave under section 16(4), as the case may be, he may request in writing (or cause a written request to be submitted to) his employer to terminate that leave.