Inspired by his own medieval tales, Conan Doyle, who had been a medic in the Boer war, believed armour would reduce the slaughter on the western front. He sent letters on the subject to David Lloyd George, the prime minister, and Sir Douglas Haig, the commander-in-chief.

The 3,000 items in the archive, to be sold by Christie??s in May, include written exchanges between Conan Doyle and his family and notebooks for many of his works. One is a sketch for A Study in Scarlet, the first Holmes story, which is expected to fetch between ??100,000 and ??150,000.

There are also letters from famous figures such as Rudyard Kipling, Oscar Wilde, Theodore Roosevelt and Winston Churchill. The collection is valued at about ??2m.

Jane Flower, manuscripts consultant at Christie??s, said it was the best archive she had seen at auction in 30 years. But the collection, which is being sold by distant relatives of the author, is likely to be broken up, with much of it going abroad.

??It??s not feasible to keep it together. There just isn??t the money in this country,?? said Flower, adding that the auction house and the vendors had approached the British Library before proceeding with the sale.

The papers, collected from the author??s study when he died in 1930, have lain for decades in the strongroom of a London solicitor awaiting the resolution of legal disputes over Conan Doyle??s legacy.

Although Conan Doyle??s body armour campaign failed, the papers show the various causes he pursued. They ranged from campaigns on behalf of prisoners sentenced to death to reform of the divorce laws, opposition to the Belgian regime in the Congo and the promotion of spiritualism, on which he spent much of the fortune he earned from Holmes.

The existence of some of the items has long been known but their whereabouts have been a mystery. These include a letter from Wilde congratulating Conan Doyle on his prose and thanking him for his own note in praise of Wilde??s novel The Picture of Dorian Gray.

??So that??s turned up at last,?? said Owen Dudley Edwards, reader in history at Edinburgh University and author of books on both writers. ??The friendship with Wilde was a very important one, he was certainly an influence on the continuation of the Holmes stories.??

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