4.—(1) Where—
(a)the whole of a member’s relevant membership period is in respect of part-time service, and
(b)the reduction under regulation B14(1)(b) is by the same proportion in respect of the whole period,
the additional membership period shall be determined in accordance with paragraphs 1 to 3 by reference to the period which would be the relevant membership period if the reduction required by regulation B14(1)(b) were not made (“the unreduced period”), and then the period resulting from the application of those provisions shall be reduced as mentioned in that regulation.
(2) Where—
(a)the whole of a member’s relevant membership period is in respect of part-time service, and
(b)different proportionate reductions fall to be made under section B14(1)(b) in respect of different parts of the relevant membership period,
the additional membership period shall be determined in accordance with paragraphs 1 to 3 by reference to the period which would be the relevant membership period if the reductions required by regulation B14(1)(b) were not made (“the unreduced period”), and then—
(i)the period resulting from the application of those provisions shall be apportioned between the different parts mentioned in sub-paragraph (b) in proportion to the respective lengths of the parts of the unreduced period attributable to each of them,
(ii)each such apportioned part of the unreduced period shall be reduced as mentioned in that regulation, and
(iii)those reduced periods shall be aggregated together.
(3) Subject to sub-paragraph (4), where part only of a member’s relevant membership period is in respect of part-time service, the additional membership period for the whole of his relevant membership period shall be determined in accordance with paragraphs 1 to 3 (and, in so far as the membership in respect of part-time service is concerned, by reference to the unreduced period), and then the period resulting from the application of those provisions (“the aggregate unreduced period”) shall be reduced by multiplying it by the fraction of which—
(a)the numerator is the member’s relevant membership period, determined, in so far as any membership in respect of part-time service is concerned, with the reduction required by regulation B14(1)(b) (and, where different proportionate reductions fall to be made under regulation B14(1)(b) in respect of different parts of the relevant membership period, determining the overall reduction as mentioned in sub-paragraph (2) above), and
(b)the divisor is the aggregate unreduced period.
(4) Where—
(a)apart from this sub-paragraph, sub-paragraph (3) would apply, and
(b)the member’s relevant membership includes not less than 13 121/365 years in respect of whole-time service,
then sub-paragraph (3) shall not apply.
(5) Where a member is in part-time service and his contractual hours are determined as mentioned in sub-paragraph (iii) of the definition of “contractual hours” in regulation B3(4), (non-cyclical fluctuation) then, for the purposes of this paragraph—
(a)the lengths of the parts of the relevant membership period by reference to which different proportionate reductions fall to be made under regulation B14(1)(b) shall be determined by reference to the periods mentioned in that sub-paragraph, and
(b)the reduction under that regulation in respect of any such period shall be made by reference to the contractual hours over that period as determined under that sub-paragraph.