Complex sentence: The highest ranking civil servant in the country is the Cabinet Secretary, a subsidiary title that was also held by the incumbent was Head of the Home Civil Service; who until recently was also the incumbent Cabinet Secretary and Permanent Secretary of the Cabinet Office.
Split into simpler sentences: The highest ranking civil servant in the country is the Cabinet Secretary. A subsidiary title that was also held by the incumbent was Head of the Home Civil Service, who until recently was also the incumbent Cabinet Secretary and Permanent Secretary of the Cabinet Office.