Sir Robert Menzies
"The Privy Council goes back to the earliest days of the Monarchy, when it comprised those appointed by the King or Queen to advise on matters of state. The Privy Council is one of the oldest parts of Government, but it has, over time, adapted to reflect the fact that the United Kingdom is a constitutional monarchy. Appointment to the Privy Council is for life."
Extract from Privy Council Office website.