It is one of Britain's most secretive, elite organisations, almost as old as the Magna Carta and with many members in their 80s and 90s. These men, appointed by the Queen – and they are almost all men – form the Privy Council, a solid, authoritative-sounding body. But it is nothing of the sort. And, at the very moment the Government is looking to this centuries-old club to help with the regulation of Britain's newspapers, its owns members question its credibility. One privy counsellor of more than 15 years' standing calls it "a myth that needs exposing".

This year will bring the appointment of the first independent regulator with the power to keep British newspapers under control. Oliver Letwin, the Cabinet Office minister, is credited with coming up with an idea that the body that would oversee the press regulator should be governed by royal charter. The attraction of this idea, to which all three of the main political parties now appear to be signed up, is that the great and the good who make sure the regulator is sticking to its brief will be more than a committee: they will be an institution. It seems that the question of who will regulate the regulator is solved.

Except that it throws up a new question: if the regulator is governed by royal charter, who governs the charter? To whom would the regulator turn if, for instance, its charter is not working out in practice and needs amending?

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There is a readymade answer, because there is nothing new about royal charters. There are 996 currently in force, the oldest being the one that governs Cambridge University, which was signed by King Henry III in 1231. The most recent charters were granted on 30 May 2012, to the Worshipful Company of Builders Merchants and the Worshipful Company of Lightmongers. All royal charters are governed by the Privy Council, so it is to the Privy Council that Cambridge University or the Lightmongers must turn if they want their charters amended. But this is where Mr Letwin's scheme runs into a problem that still needs sorting out, urgently.

The Privy Council is a façade. One privy counsellor confesses to having attended just one working Privy Council meeting, from which he came away with no real idea of what they had decided.

On the rare occasions that something crops up that requires a Privy Council decision, the Lord President – currently Nick Clegg – contacts the Palace, and turns up with a quorum, which can be as few as three other privy counsellors, who can all be serving politicians from the governing party, and together they go through the ritual of signing the necessary documents.

To be a privy counsellor is an honour that entitles the holder to put the words Right Honourable in front of his or her name. It is not a job. There are, by my count, 606 of them, many of whom will not have been to a Privy Council meetings for decades. The one who has been a privy counsellor longest is the Duke of Edinburgh, a member since 1951. Next in seniority is 93-year-old Lord Carrington, who became a privy counsellor when Harold Macmillan appointed him First Lord of the Admiralty in 1959. The doyen of the Commonwealth politicians on the Privy Council is 84-year-old Sir Toaripi Lauti, who was the first Prime Minister of Tuvalu. The first woman member from a former colony was Helen Clark, from New Zealand.

Like a peerage, privy counsellorship is for life – with rare exception. After the former Labour MP Elliott Morley was sent to prison for fiddling his expenses, he suffered the additional penalty of being the first person in 90 years to be expelled from the Privy Council.

There is an induction process for new members, vividly described in Tony Benn's diaries. He did not want to go through it, in 1964, but was told that unless he did, he would never be allowed to see Cabinet papers.

"We were summoned one by one in the Queen's drawing room. She shook us by the hand, then we stood in a row as the oath was administered," he wrote. "We then went up to the Queen, one after another, kneeling and picking up her hand and kissing it, and then bowing…I left the Palace boiling with indignation and feeling that this was an attempt to impose tribal magic."

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One of the most recent members said that he has been to two meetings in six years. One was his induction; the other involved decision making. "It was when a university wanted to change its name, and I think there might have been some other piece of business," he said. "I'm not sure I really understood what we were signing: it was very uncontroversial. There were six of us, all Labour, and the Queen. We all stood, but the meeting did not last long enough to tire out any of our ageing legs."

Another privy counsellor, of 15 years' standing, said: "It's a myth that needs exposing. I get letters about it. It's a device that lets civil servants take decisions and say that they are taken by the Privy Council. It hasn't met for at least 25 years. They only keep our phone numbers because the council will have to meet when the Queen dies. I'll go to that one because it'll be something to tell the grandchildren. They'll have to wheel some of the older members in."

The system has worked because all 996 royal charters currently in force are uncontroversial – unlike a royal charter governing a press regulator. The idea that the charter can be administered by a body with more than 600 members, some in their 90s, is absurd; while the current practice of allowing the Lord President to summon a handful of his party colleagues and call that a Privy Council meeting, with the authority to change the rules for regulating the press, would be an outrage. Consequently, 2013 could be the year when the centuries-old Privy Couwncil opens its doors to a cold blast of change.

Queen's advisers: Members of the Privy Council

Prince Philip, 90

Appointed to the Privy Council by King George VI on 4 November 1951, the Duke of Edinburgh has been a member longer than anyone else alive.

Lord Carrington, 93

Appointed by Harold Macmillan in 1959, he is the only other living member to have completed a half century.

Geoff Hoon, 59

A lobbying scandal means the former Defence Secretary can't hold a Commons pass until December 2015. That does not stop him being a privy councillor.

Sir Toaripi Lauti, 84

The oldest of the New Commonwealth privy councillors, appointed in 1979, when he was Prime Minister of the newly independent Tuvalu.

Margaret Thatcher, 87

The Privy Council was almost an all-male body when she joined in 1970. She is the senior woman member, though too frail to attend.

Tony Benn, 87

The former Labour MP did not want to join the Privy Council in 1964, but was told he had no choice and is still officially a member.