7SA person who at the commencement of section 124 of this Act is detained in a detention centre by virtue of a custodial order—
(a)under section 71 AA of the M1 Army Act 1955, section 71AA of the M2 Air Force Act 1955 or section 43AA of the Naval Discipline Act 1957; or
(b)under paragraph 10 of Schedule 5A to the Army Act 1955, Schedule 5A to the Air Force Act 1955 or Schedule 4A to the M3 Naval Discipline Act 1957,
shall be detained in such young offenders institution as the Secretary of State may direct, and any enactment applying to persons detained in young offenders institutions shall apply to a person so detained under this paragraph.