6The [1955 c. 19.] Air Force Act 1955 shall continue to apply without the amendments made by paragraph 5 in relation to any airman who is in service immediately before the date on which that paragraph comes into force unless—
(a)he re-enters, re-engages or extends his air-force service after that day; or
(b)he elects irrevocably in such manner as may be prescribed to be a person to whom that Act shall apply with those amendments.