6. A person’s service shall comprise all of the periods which at the date on which he ceased to hold an employment or appointment mentioned in regulation 3(1), or on which the emoluments of such employment or appointment were reduced, as the case may be, fell within any of the following descriptions, but no period shall be taken into account under more than one description—
(a)any period during which he held such employment or appointment;
(b)any period of employment that would be taken into account for any purpose of a relevant pension scheme; and
(c)any other period that the Department may approve in any particular case.