The only copy of Magna Carta in private hands sold for $21.32 million (£10.6 million) this morning in the first auction of the “birth certificate of freedom”.

The 1297 example, described as the most important document to come up for sale, was acquired by David Rubenstein, the founder of the Carlyle Group, at Sotheby’s in New York. He has paid $8,528 a word.

Sotheby’s had put a pre-sale estimate on the document of $20-$30 million.

The 14in-by-16in (35.6cm-by40.6cm) sheet of animal-skin vellum is one of only 17 originals of the founding “Great Charter” of English liberties first signed by King John at Runnymede — near present-day Staines, Surrey — in 1215.

The document established the principle of habeas corpus, which protects people against unlawful imprisonment by ensuring such rights as trial by jury and freedom from unlawful arrest.

Clause 39 proclaims: “No free man shall be taken or imprisoned or disseised or outlawed or exiled or in any way ruined, nor will we go or send against him, except by the lawful judgment of his peers or by the law of the land.”

Four of the surviving 17 copies date from the reign of John, eight from that of Henry III and five from that of Edward I. The Sotheby’s example bears the wax seal of King Edward I hanging from a ribbon at the bottom of the parchment — one of only five that still carry the royal seal.

1297 was the year that Magna Carta was formally entered into the statute rolls as the law of England. It came into being as a result of a dispute between King John and the English barons and went some way towards limiting the authority of the king.

The only other original outside Britain was a gift by the country to “The People of Australia”. It is on display at the Parliament in Canberra.

Mr Rubenstein, the founder of the Carlyle private equity group and a former deputy domestic policy adviser to President Carter, said that he would put the document back on public view at the National Archives in Washington, where it had been on loan.

“I thought it was very important that the Magna Carta stay in the United States, and I was concerned the only copy in the United States might escape the United States as a result of this auction,” he said.

“I am a person who has served in government myself. I worked in the White House as a young man. At that time I recognised the importance of these kind of documents and the importance of freedom.”

He admitted that he could not actually read it because he had avoided learning Latin at school — a decision he now regrets.

The 2,500-word document, written in medieval Latin, was put up for sale by the Texan software billionaire and two-time independent presidential candidate Ross Perot.

Mr Perot acquired it for $1.5 million in 1984 from relatives of James Thomas Brudenell, the 7th Earl of Cardigan, who led the Charge of the Light Brigade during the Crimean War. Magna Carta had been at the Brudenells’ family seat at Deene Park, Northamptonshire, for more than half a millennium.

In a catalogue essay Professor Nicholas Vincent of the University of East Anglia theorises that the Brudenells obtained it in Buckinghamshire after William Brudenell, the founder of the family’s fortunes, married an heiress there during the reign of Edward III.

After displaying Magna Carta at Independence Hall in Philadelphia, Mr Perot loaned it to the US National Archives in Washington, where it has been seen by a million people.

“It’s in remarkable condition for a document that dates from 1297,” Chris Rudy Smith, an archivist at the institution, said before the sale.

Proceeds of the sale will go to Mr Perot’s foundation to make funds available for medical research and care for wounded military veterans.

$8,528

Or £4,233 — the cost per word of buying the only edition of Magna Carta in private hands. A copy of J. K. Rowling’s The Tales

of Beedle the Bard was sold at auction for £1.9 million last week, or for £363.64 a word

Source: Times database

Times Recommends

• Congo's rangers risk their lives to guard gorillas
• Pearl farming in China losing its lustre
• Axl Rose mystery as album arrives at last