2.—(1) A person is an exempt individual on a particular day if–
(a)at any time on the day he is imprisoned, detained or in custody under the Army Act 1955(1), the Air Force Act 1955(2) or the Naval Discipline Act 1957(3), and
(b)the conditions mentioned in paragraph (2) below are fulfilled with respect to the time where they are applicable.
(2) The conditions are that, where the person is in custody under arrest–
(a)he is not in custody under open arrest; and
(b)the custody forms part of a continuous period exceeding 48 hours during which he is under arrest.
(3) A person is to be treated as in custody under open arrest for the purposes of paragraph (2)(a) if he is so treated for the purposes of Queen’s Regulations for the Navy, Army or Air Force.