Scotland secures historic ‘crown jewels’
The Melville papers - which include the documents of Henry Dundas, 1st Viscount Melville - contain about 11,000 records which span 150 years.
The National Records of Scotland purchased the collection for £1.35m.
For three decades Dundas was the Grand Manager of Scotland, or Great Tyrant to his enemies, and the trusted lieutenant of British prime minister William Pitt.
He was the most powerful man in 18th Century Scotland.
After training as a lawyer, he was appointed Solicitor-General at the age of 24 and Lord Advocate at 33 but moved into politics.
He was a crucial figure in the expansion of British influence in India, and dominated the East India Company.
Dundas promoted harsh punishment for rebellious colonists in the Americas and prolonged the abolition of slavery.
He was the last person to be impeached in the United Kingdom, for misappropriation of public money, in 1806. He was acquitted, but never again held office.
Effigies of Dundas, known as "the uncrowned king of Scotland", were burned rather than those of the King during the political and social unrest that accompanied the outbreak of revolution in France.
He is commemorated by the 150-foot high Melville Monument, designed by William Burn in 1823, in Edinburgh's St Andrew Square.
His papers have been on long-term loan to the archives but have now been bought from the Melville family for the permanent collection.
George MacKenzie, Keeper of the Records of Scotland, said: "Had we not acquired it for Scotland's archive, the papers would have been sold at auction at a price beyond the public purse and broken up and dispersed across the world.
"The Melville papers have been extensively used by the public since they were first loaned to us, and now that they're in public ownership, we'll be working hard to make them even more widely available."
The collection includes letters from economist Adam Smith, a copy of Admiral George Cockburn's journal which detailed Napoleon's last journey into exile and correspondence relating to the reform of Scotland's political system.
Richard Finlay, Professor of Scottish History at the University of Strathclyde, said the purchase was a major coup for the National Records of Scotland.
"The papers cast a considerable amount of light on the expansion of the British state and empire in the late eighteenth and early nineteenth century by giving us an insight into the activities of one of the key architects of the projection of British world power in this era.
"Henry Dundas was a man who was at the centre of a web of patronage that cast itself around the earth. The Dundas dynasty was Scotland's greatest and most powerful political family since the Stuart monarchy."
Culture minister Fiona Hyslop said: "There are very few important politicians and military and naval men of the time who did not have dealings with the Dundases.
"Their influence over the government, politics and society of Scotland was extensive - and their legacy lives on Scottish public life today, in our street names, our statues and now, in this public collection."