Some 155 years ago, a 9-year-old boy carrying a silk cushion was brought before Queen Victoria. His job was simple: To present Britain with the most glittering and symbolic spoil of its war to subjugate the Indian subcontinent.
The boy was the Duleep Singh, the last Sikh ruler of the Punjab, and the prize his new imperial masters had made him travel 6760km to deliver by hand was the Koh-i-Noor diamond - the mysterious and terrible stone of emperors.
The 186-carat gem, whose name means Mountain of Light in Farsi and which was described by one Mughal emperor as being "worth half the daily expense of the whole world", carried with it a curse and a 750-year bloodstained history of murder, megalomania and treachery.
But its passage to Britain in 1851 carried a different meaning: it was a carefully choreographed exercise in establishing the majesty of the Raj - and the one-way flow of material riches from it.
Lord Dalhousie, the Governor-General of India, ordered that Prince Duleep, London's new puppet Maharajah of Lahore, deliver the Koh-i-Noor in person.
The diamond was war booty and its delivery was to be a spectacle carried out in much the same manner as the tribute paid by defeated enemies of Egyptian pharaohs and Roman emperors. It was the centrepiece of the Great Exhibition of 1851, attracting thousands of visitors.
In a letter to a friend in 1849, the Viceroy wrote: "My motive was simply this: That it was more for the honour of the Queen that the Koh-i-Noor should be surrendered directly from the hand of the conquered Prince into the hands of the sovereign who was his conqueror, than it should be presented to her as a gift."
It was perhaps with these words echoing in their ears that 127 years later, British diplomats began the delicate task of dealing with a forceful request from Pakistan - on whose territory the Koh-i-Noor was surrendered - that the diamond be returned.
Secret government papers just released under the 30 year rule at the National Archives in Kew, West London, detail how in 1976 officials at the Foreign Office formulated a firm rebuttal to the Pakistani claim on what had literally become a jewel of the British Crown.
Prince Albert, Victoria's husband, spent the then astronomical sum of £8000 on having the Koh-i-Noor re-cut - at a cost of 40 per cent of its weight, slimming it down to 105 carats - after complaints at the Great Exhibition that the imperial prize was lacking in lustre.
It was set into the Imperial Crown and since 1911 the diamond has been worn in crowns sported by the female consort to the monarch, including the late Queen Mother, who wore it for her husband's coronation in 1937 and for her daughter's coronation in 1953.
The demand for the restoration of the diamond came from the Pakistani Prime Minister, Zulfikar Ali Bhutto, in a letter to his British counterpart, James Callaghan.
Dated August 13, 1976, the letter began: "I am writing to you shortly before our annual Independence Day. This occasion never fails to bring to mind Pakistan's historic grievances about the disposition of territories and assets to which we were entitled upon the termination of British rule."
Evoking the "immense sentimental value" of the diamond to Pakistan, Bhutto continued: "Its return to Pakistan would be a convincing demonstration of the spirit that moved Britain voluntarily to shed its imperial encumbrances and lead the process of decolonisation. "Indeed, it would be symbolic of a new international equity strikingly different from the grasping, usurping temper of a former age."
The response from the Foreign Office diplomats, at least on a private level, would have made Lord Dalhousie proud.
An internal memo from one senior civil servant in the secret papers made it clear that, whatever the diplomatic or legal niceties, Britain considered possession to be nine-tenths of the law.
It read: "The stark facts are these: i) We have the Koh-i-Noor diamond, whether or not our possession of it is legally justified. ii) We have made it clear that we are keeping the diamond, adducing the best arguments to support our contention."
The final response was expressed in more diplomatic language and made use of the fact that, such is the allure and mystique of the diamond, at least a dozen emperors, maharajahs, sultans and governments had been prepared to indulge in rare savagery and deceit to obtain it.
Advisers to Callaghan pointed out that the 1849 Treaty of Lahore, drawn up by Lord Dalhousie to formalise British rule in Punjab, contained a clause formally surrendering the Koh-i-Noor to "the Queen of England".
They also suggested that its passage over the centuries through owners from the Delhi sultanate to the Persian shah meant there would be competing claims for ownership from Iran, Pakistan and India.
Replying to Bhutto, Callaghan said: "I need not remind you of the various hands through which the stone has passed over the past two centuries, nor that explicit provision for its transfer to the British Crown was made in the peace treaty with the Maharajah of Lahore which concluded the war of 1849.
"In the light of the confused past history of the Koh-i-Noor diamond, the clear British title to it and the multiplicity of claims which would undoubtedly be made to it if its future were ever thought to be in doubt, I could not advise Her Majesty the Queen that it should be surrendered to any other country."
The spat was only the latest in a bloody succession of battles for a gem stone which has been the embodiment of the supremacy of force - and a harbinger of ill fortune - throughout its history.
The Koh-i-Noor was mined in India in around 1100 and probably originated from Golconda in the southern region of Andhra Pradesh.
The shape and size of a small hen's egg, the diamond rapidly attained a sinister mystique.
It is probably not entirely coincidental that the Koh-i-Noor is reserved for use in crowns used by a female member of the British royal family.
A Hindu text from the time of Koh-i-Noor's first authenticated appearance in 1306 states that the stone carries a curse lethal to any male owner.
The hex read: "He who owns this diamond will own the world, but will also know all its misfortunes. Only God or a woman can wear it with impunity."
By the 16th century, the stone had fallen into the hands of the first Mughal emperor, Babur, whose son was the first to fall foul of the "curse" by being driven from his kingdom into exile.
The later Mughal ruler Shah Jahan, who built the Taj Mahal, had the diamond placed into the famous Peacock Throne of the dynasty but spent his last days, according to legend, watching its reflection through a barred window after being imprisoned by his son, Aurangazeb.
It was only after the mughals had been deposed and control of the diamond passed to the Persians that the Koh-i-Noor got its present-day name.
The story has it that Nadir Shah, the conqueror of the mughals, was preparing to return home after sacking Delhi in 1736 when he realised that the great diamond was missing from his booty.
He was supposedly tipped off by a disenchanted member of the mughal emperor's harem that his enemy kept it hidden in his turban.
Using an old war custom, Nadir Shah proposed an exchange of turbans, which the defeated ruler could not refuse. As the gem fell to the ground from the unfurling cloth and caught the light, Nadir Shah is said to have proclaimed: "Koh i noor."
Rather like the "Precious" ring in J.R.R. Tolkien's trilogy, the diamond has ever since been lusted after by its owners, who have been hypnotised by its value and status.
As one of Nadir Shah's courtiers put it: "If a strong man should take five stones and throw one north, one south, one east and one west, and the last straight up in the air, and then the space between filled with gold and gems, that would equal the value of the Koh-i-Noor."
After the assassination of Nadir Shah, another victim of the curse, the diamond passed through the hands of his successors, each dethroned and ritually blinded, until it was passed in return for sanctuary to Ranjit Singh, the Lion of Lahore, self-declared ruler of Punjab and father of Duleep Singh.
Within 40 years, the stone had passed into the possession of Lord Dalhousie after a military campaign every bit as ruthless and blood-soaked as those which had previously been fought for possession of the Koh-i-Noor.
Some historians have pointed out that as the stone has spent 155 years in the possession of British monarchy, the present Queen can claim to be one of the longest-standing owners of the Koh-i-Noor. It is kept in the Tower of London as part of the Crown Jewels collection now worth an estimated £13 billion ($36 billion).
But despite Callaghan's rebuttal to Pakistan 30 years ago, the attraction of the diamond remains undimmed for its international suitors.
Both India and Pakistan, keen to resurrect the wrongs of the colonial era in the name of their present rivalry, have made regular competing claims. The former Indian High Commissioner to London accused Britain of "flaunting" the riches of empire when the Queen Mother's 1937 Coronation Crown was carried atop her coffin in 2002.
The mere suggestion last year that the same crown may eventually pass to Camilla, the Duchess of Cornwall, should her husband become King, was enough for New Delhi to renew its request.
A spokesman for the High Commission in London said: "The Indian Government has a legitimate claim on the diamond. We hope to resolve the issue as soon as possible."
Behind closed doors in Whitehall, it is unlikely that the position outlined 30 years ago has changed.