4.—(1) For the purpose of this Schedule, a person (P) is eligible to be an active member of the NFPS on a given date if on that date P is not in pensionable service under the FPS or the NFPS and either—
(a)P is in service as a firefighter which entitles P to be eligible to be an active member of the NFPS; or
(b)P is on a gap in pensionable service not exceeding five years.
(2) For the purpose of sub-paragraph (1)(b), after the scheme closing date P is not on a gap in service while P is in pensionable public service.