An agency or Minister may extend the period referred to in paragraph 15(5)(b) for dealing with a request, or that period as extended under subsection 15(6) or (8) (consultation), by a further period of no more than 30 days if:
(a) the applicant agrees in writing to the extension; and
(b) the agency or Minister gives written notice of the extension to the Information Commissioner as soon as practicable after the agreement is made.