29.—(1) A person who is—N.I.
(a)required to undertake essential or emergency work in the United Kingdom, or
(b)returning from undertaking such work outside of the United Kingdom, where a government department has certified P's work as necessary to facilitate essential government work or essential state business.
(2) For the purposes of sub-paragraph (1) “essential government work” and “essential state business” have the same meaning as in paragraph 24.