15.—(1) A person who is a Crown servant, a government contractor, or a member of a visiting force, who—N.I.
(a)is required to undertake work necessary to the delivery of essential defence activities,
(b)has travelled from a point of origin within the common travel area or from a green list country on a vessel or aircraft operated by, or in support of, Her Majesty's armed forces or by, or in support of, a visiting force and that vessel or aircraft has not taken on any persons, docked in any port or landed in any red list country or amber list country, or
(c)has undertaken a continuous period of at least 10 days ending with the day immediately preceding the day of their arrival in the United Kingdom aboard a vessel operated by or in support of Her Majesty's Naval Service or by, or in support of, a visiting force, where they have not disembarked and that vessel has not taken on any persons or docked in any port outside of the common travel area for a period of at least 10 days ending with the day of its arrival in the United Kingdom.
(2) For the purposes of sub-paragraph (1)—
(a)“defence” has the meaning given in section 2(4) of the Official Secrets Act 1989,
(b)“visiting force” means any body, contingent or detachment of the forces of a country, being a body, contingent or detachment for the time being present in the United Kingdom (including United Kingdom territorial waters), on the invitation of Her Majesty's Government in the United Kingdom.