A shaft of light was cast last week on the Privy Council, one of the most obscure and unknown parts of the British constitution and hidden parts of the justice system.

The law lords who sit as the Privy Council's Judicial Committee ruled that a gallantry medal established by the Queen for Trinidad and Tobago was unconstitutional because it discriminated against non-Christians.

But what is the Privy Council - and its court? A recent report by Justice, the law reform body, says that “the lack of accessibility and transparency of the Privy Council means that almost no one understands its processes”.

The Council is a body of advisers to the Queen dating back to feudal times when the monarch ruled by divine right. Yet the Privy Council and its court are far from a relic of history.

Until recently, its members took precedent over other MPs whom the Speaker might call on to speak - and they could speak for longer. They also take precedence after Knights of the Garter and of the Thistle when it comes to ceremonial hierarchy.

More important, though, Privy Counsellors can make orders that bypass Parliament, while still having the same force as democratically passed laws. And their laws don't have even have to carry a statement that they comply with the European Convention on Human Rights.

Meanwhile, its court, the Judicial Committee, operates away from the public eye, in a little-visited room off Downing Street. But it has the power to save a person from death or, for instance, as in its recent ruling, to dispossess Chagos Islanders from their homes.

As Roger Smith, the director of Justice, put it in his forward to a Justice report: “Many people may have heard of its judicial committee, but its other roles emerge from the constitutional fog only occasionally.”

The Privy Council’s continued existence, he added, is “regarded as vaguely charming and largely formal”. But it can still display “the power that once it had more widely as an instrument of feudal rule”.

The Justice report, a fascinating expose by Patrick O’Connor, QC, of Doughty Street Chambers, notes that even the statutory definition of the Privy Council is circular: it is defined as the members of “Her Majesty’s Most Honourable Privy Council”.

The term was first coined under Henry V in the early 15th century; by then it had had jurisdiction to deal with finance, aliens and trade, the church and preservation of the King’s Peace. By 1487 its judicial function became the infamous Court of the Star Chamber, specialising in supervising the press and public morality.

Who are Privy Counsellors? Currently there are more than 540, mostly senior politicians who were once MPs. As with a gentlemen’s club or secret society, members swear allegiance to the Queen and to “assist and defend...against all Foreign Princes”.

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