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

has travelled 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, immediately before the person's arrival, been aboard a vessel operated by or in support of Her Majesty's Naval Service F3or by, or in support of, a visiting force for a continuous period of at least 14 days and that vessel has not taken on any persons or docked in any port F4in a non-exempt country or territory during that period.

“defence” has the meaning given in section 2(4) of the Official Secrets Act 1989 M1,

“visiting force” means a visiting force within the meaning given in section 12(1) of the Visiting Forces Act 1952 M2, 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 M3, or which is a country member of the North Atlantic Treaty Organisation.