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 14 days immediately preceding their arrival aboard a vessel operated by or in support of Her Majesty's Naval Service F3or by, or in support of, a visiting force 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 14 days immediately preceding its arrival in the United Kingdom.

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

“visiting force” means a visiting force within the meaning given in section 12(1) of the Visiting Forces Act 1952 M1, where that force is from a country which is listed under section 1(1)(a), or designated under section 1(1)(b) or 1(2) of the Visiting Forces Act 1952, or which is a county member of the North Atlantic Treaty Organisation.