During the Labour leadership race, there was some speculation that Jeremy Corbyn, a staunch republican, might refuse to become a Privy Counsellor if he won the election. But lo and behold, Corbyn decided to become right honourable after all. This really shouldn’t surprise anyone.
The idea that Corbyn could refuse a Privy Counsellorship seems to be based on the notion that it’s nothing but an honorific, which isn’t entirely true. The Privy Council is still an active body, though nowadays its proceedings are entirely formal in nature. Although the vast majority of Privy Counsellors will play no role in its work, membership in the Council does have political implications. Most notably, you have to be a Privy Counsellor in order to be a Cabinet minister. This is both a matter of convention and a matter of law. The Promissory Oaths Act 1868 says that senior ministers (including the Prime Minister) must take the Oath of Allegiance and Oath of Office in the presence of the Queen in Council.
If a non-Privy Counsellor is appointed to the Cabinet, they must be appointed to the Council before they take their oaths of office. When Ramsay Macdonald became the first Labour Prime Minister in 1924, he was not yet a Privy Counsellor. The result was a rather awkward ballet in which George V admitted MacDonald to the Council first, then asked him to become Prime Minister several hours later. In order to avoid this hassle, modern Prime Ministers automatically recommend Privy Counsellorships for the leaders of the other major parties.
Since Corbyn presumably wants to be Prime Minister some day, he had little choice but to accept a Privy Counsellorship. In theory, he could have refused to accept it until he was on the cusp of entering Number 10, but that would only create administrative hassle. Also, Corbyn would presumably have been left out of the confidential briefings that the Leader of the Opposition customarily receives from the Government since they are ‘on Privy Council terms.’ Corbyn might think that the Privy Council is a lot of nonsense, but for the moment, he must go along with it.
 Once a month or so, three or four Privy Counsellors join the Queen wherever she may happen to be in order to make Orders in Council. There is no discussion or debate—the Lord President of the Council simply reads a list of Orders and Her Majesty simply says “approved” from time to time.
 Privy Council membership is for life (unless you resign), but only Privy Counsellors who are members of the current Government are summoned to attend meetings. There doesn’t seem to be much rhyme or reason to the summonses; I suspect it’s largely a matter of who is nearby and available.
 Technically, the Act refers to the ‘First Lord of the Treasury’ and not the ‘Prime Minister,’ but there is of course a longstanding convention that those offices are held by the same person.
 Rodney Brazier, Ministers of the Crown (New York: Oxford University Press, 1997), 82.
 This practice began in 1961 under Harold Macmillan.