(b) During any period between his or her leaving the public service for the purposes of serving in Her Majesty's Forces and the date of his or her commencing military service, he or she shall, for the purposes of this Act, be deemed to be on leave without pay, not granted on grounds of public policy, from the public service in which he or she was last employed, and to have held the substantive office last held by him or her in that service, prior to military service and during any period between the termination of his or her military service and the date of his or her re-entering the public service he or she, for the said purposes, is considered to be on leave as aforesaid from the service, and to have held the substantive office, in which he or she is re-employed.