13D.—(1) If, after the date on which an agreement referred to in section 13C(1)(b)(i) is signed by the employer and the employee (whether or not the approved flexible working arrangement to which it relates has commenced), the employer and the employee so agree, in writing—

(a) the flexible working arrangement or part of it may be postponed to such time as may be agreed to,

(b) the period of the flexible working arrangement may be curtailed in such manner and to such extent as may be agreed to, or

(c) the form of the flexible working arrangement may be varied in such manner as may be agreed to,

and in such a case the agreement referred to in section 13C(1)(b)(i) shall be deemed to be amended accordingly.

(2) If, after the date on which an agreement referred to in section 13C(1)(b)(i) is signed by the employer and the employee and the flexible working arrangement has not commenced, the employee concerned becomes ill or incapacitated such that the employee is unable to care for the person who is the subject of an approved flexible working arrangement, the employee may, by notice in writing given to the employer concerned, as soon as is reasonably practicable after becoming ill or incapacitated, and accompanied by the relevant evidence in respect of the illness or incapacity, postpone the commencement of the flexible working arrangement to such time as the employee is no longer ill or incapacitated, and in such a case the agreement referred to in section 13C(1)(b)(i) shall be deemed to be amended accordingly.

(3) In subsection (2), "relevant evidence", in relation to an employee, means—

(a) a medical certificate—

(i) stating that the employee named in the certificate is, by reason of the illness or incapacity specified in the certificate, unable to care for the person named in the certificate, and

(ii) signed by a registered medical practitioner within the meaning of section 2 of the Medical Practitioners Act 2007,

or

(b) if the employee does not have a medical certificate referred to in paragraph (a), such evidence as the employer concerned may reasonably require in order to show that the employee is, by reason of illness or incapacity, unable to care for the person concerned.]