20.—(1) A person, who is eligible to be an active member of this scheme but is not in pensionable service under this scheme, may opt at any time to become an active member, subject to the following provisions of this regulation.
(2) Unless the scheme manager specifies, a person may only exercise the option under paragraph (1) once during any period of 12 months.
(3) The option may only be exercised by notice in writing to the person’s commanding officer in such form as the scheme manager requires.
(4) For the purposes of this regulation, the option is treated as having been exercised on the date on which it is received by the person’s commanding officer.
(5) A person who exercises the option becomes an active member on the date on which the option is exercised or at such other time as the scheme manager considers appropriate.