17.—(1) This paragraph applies if the person becomes entitled to payment of retirement benefits by virtue of regulation E4(4) or (5) (incapacity).
(2) For the purposes of regulation E8 (enhancement) the appropriate period shall be calculated by reference to the aggregate of the period counting as reckonable service in relation to the earlier employment and the period so counting in relation to new employment, and—
(a)if he becomes entitled to payment of the benefits within 3 years after the start of new employment, the period counting as reckonable service in relation to the earlier employment; or
(b)in any other case, the period so counting in relation to new employment,
is increased by the appropriate period so calculated.