Monday marks the 800th anniversary of Magna Carta and is regarded by many as laying the foundations for modern democracy, protecting freedoms and defending personal liberty.
On June 15, 1215, on the banks of the Thames, in Runnymede, King John met with a rebel group of English barons and placed his seal the document.
Today, the Prime Minister joined the Queen and the Archbishop of Canterbury to celebrate the 800th anniversary, but in 2012 he was unable to explain what Magna Carta actually was.
A fact not lost on many people today.
US TV September 2012.
David Letterman: “The literal translation of Magna Carta is what?”
David Cameron: “Again, you are testing me.”— Patrick Wintour (@patrickwintour) June 15, 2015
I expect David Cameron to talk about how wonderful Magna carta is though obviously he hasn't read it he#MagnaCarta800th #humanrights— muttleyashworth (@muttleyashworth) June 15, 2015
David Cameron champions Magna Carta but in 2012 he didn't know what it meant when he appeared on David Letterman's Late Show …— Equity (@EquityxD) June 15, 2015
American chat show host David Letterman asked Cameron what the literal translation of Magna Carta was. Cameron said: “Again, you are testing me.”
Letterman replied: “Oh it would be good if you knew this.” Cameron said: “Yeah, well it would be.”
Cameron's lack of clarity on Magna Carta in 2012 didn't help the Prime Minister as he drew a parallel between the historic charter and the Human Rights Act - which he pledged to scrap in the face of huge opposition from legal experts.
In Cameron's speech at Runnymede today, he said: "For centuries, [Magna Carta] has been quoted to help promote human rights and alleviate suffering all around the world.
"But here in Britain, ironically, the place where those ideas were first set out, the good name of ‘human rights’ has sometimes become distorted and devalued.
"It falls to us in this generation to restore the reputation of those rights – and their critical underpinning of our legal system.
"It is our duty to safeguard the legacy, the idea, the momentous achievement of those barons and there couldn’t be a better time to reaffirm that commitment than on an anniversary like this."
Not everyone was entirely convinced the prime minister had got his timing or tone right. Labour's shadow justice secretary lambasted Cameron for using the anniversary to "attack fundamental rights".
Lord Charles Falconer said: "David Cameron claims he is safeguarding the legacy of Magna Carta but his own plans would scrap people’s basic rights and threaten the UK’s standing in the world.
"If the Prime Minister was serious about safeguarding the legacy of Magna Carta he wouldn’t be using its anniversary to attack fundamental rights.
"David Cameron should drop any plans to repeal the Human Rights Act and to withdraw from the European Convention on Human Rights immediately."
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Director of civil liberties campaigners Liberty Shami Chakrabarti added: "The Prime Minister could give a masterclass in bare-faced cheek, using Magna Carta day to denigrate our Human Rights Act.
"But we will take no lessons in rights and freedoms from a leader who wants to dilute them to the detriment of everyone in the UK and wider watching world."
Guardian cartoonist Martin Rowson was also unimpressed with Cameron's tone.
The Cameron caricature is sat in front of some parchment which says that he will enshrine the "inalienable right of all free peoples everafter to neverending budget surpluses and no tax rises (unlike Labour tee hee)."
An American flag with arms has a sword poised behind Cameron's back. Secretary of State for Justice, Michael Gove, holds a torn-up 'legal aid' document and is standing on the Human Rights Act, which has been left on the muddy floor.