4.—(1) Where—
(a)a former professional fireman not subject to the Act of 1925, not being a person in whose case the National Fire Service (Preservation of Pensions) (General Pension Funds) Regulations, 1941(1), had effect immediately before he ceased to be a member of the National Fire Service, or
(b)a person, not being a former professional fireman, who was employed in the National Fire Service immediately before the appointed day and to whom the Police Pensions Act, 1921, applied immediately before the said day,
not later than one month after the said day enters upon employment under a local authority otherwise than as a member of a fire brigade, he shall, if within three months after he enters upon such said employment he so elects by notice in writing served upon the said authority, be entitled to reckon, in the proportion provided in paragraph (2) of this Regulation, all his approved service under the relevant pension provisions, or, as the case may be, all his approved service within the meaning of the said Police Pensions Act, 1921, as, if that authority are not a local Act authority, contributing service under that authority, or, if that authority are a local Act authority, as local Act scheme service under that authority.
(2) The proportion in which such approved service as aforesaid shall be reckoned is as follows, that is to say, three years of such approved service shall be reckoned as equivalent to four years of such contributing service as aforesaid, or, as the case may be, to four years of such said local Act scheme service, and any other period of such approved service shall be reckoned in the same proportion.
I, p. 325.