is required to undertake work necessary to the delivery of essential defence activities, F1...

has travelled from a point of origin within the common travel area or from an exempt country or territory 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 non-exempt country or territory, or

has undertaken a continuous period of at least F810 days F4ending 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 F3or by, or in support of, a visiting forceF5, 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 F810 days F6ending with the day of its arrival in the United Kingdom.

“defence” has the meaning given in section 2(4) of the Official Secrets Act 1989,

“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.