The Privy Council is one of the most obscure and murky corners of the British constitution — yet its powers are far from antiquated or redundant.

They can range from commuting the death penalty on prisoners in the Caribbean to dispossessing the Chagos Islanders of their homes.

Her Majesty’s Most Honourable Privy Council is a body of advisers to the monarch, whose members are chiefly senior politicians who were members of the Commons or Lords, including bishops and hereditary peers. Like a gentlemen’s club or secret society, its (life) members swear allegiance to the Queen and to “assist and defend . . . against all Foreign Princes”. Their task is to advise the sovereign on the exercise of the Royal Prerogative, her personal powers, and to carry them out on her behalf.

Alongside archaic and seemingly quaint powers they can still uphold or quash a death sentence; grant royal charters; or appoint the chairman of the BBC. But the Privy Council also has its own court, the Judicial Committee, which acts as the final court of appeal for many former colonies and UK overseas territories. These are mainly in the Caribbean but also include appeals from the Channel Islands and the Isle of Man, Admiralty appeals from the Cinque Ports and disciplinary appeals involving doctors and dentists as well as some appeals from ecclesiastical courts. Since 1998 it can rule on constitutional appeals arising over devolved powers to Scotland and Wales.

Who sits in this powerful court that has its origins in medieval times, and which under Henry VII became the infamous Court of Star Chamber, left — described by one historian as a “whipping, nose-slitting, ear-cropping court; a court with a grim, unseemly humour of its own”?

They are the same 12 law lords who make up Britain’s highest court, namely the Appellate Committee of the House of Lords.

At present they sit in a little-known court off Downing Street, but this autumn will sit in a court in the new supreme court building in Parliament Square. They handle about 55 to 65 Commonwealth and devolution appeals a year, appeals that are nominally to the Queen as head of state. In recent years their overseas jurisdiction has declined as successive countries have cut off the Privy Council as a court of final appeal: Canada, India, Sri Lanka, African nations, Malaysia, Singapore and most recently Hong Kong and New Zealand have all withdrawn.

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