An archive of more than 3,000 letters, notes and manuscripts belonging to the creator of Sherlock Holmes has been discovered 74 years after his death.

The collection, now valued at £2 million, was amassed by Scots-born author Sir Arthur Conan Doyle before his death aged 71 in 1930 at Windlesham Manor, his home in Crowborough.

Never before seen in public, the lost archive has only recently surfaced in a strongroom at a firm of London lawyers.

The papers are being auctioned by London-based Christie's in May.

Included are exchanges between Conan Doyle and his family as well as notebooks containing early drafts.

One includes a sketch for A Study In Scarlet, the first of his Sherlock Holmes stories, which is expected to fetch up to £150,000.

It has the original title, A Tangled Skin, crossed through and was written when he was a struggling young doctor in Southsea, Portsmouth, in the 1880s.

Other letters are from famous figures including Winston Churchill, Oscar Wilde, P G Wodehouse, Theodore Roosevelt and Rudyard Kipling.

The individual letters' values are estimated at between £1,000 and £10,000.

Tom Lamb, Christie's head of books and manuscripts, said: "Opening the dozen or so large cardboard boxes was a spine-tingling moment I will never forget."

The existence of some items, such as a letter from Wilde praising Conan Doyle's prose, has long been known but their whereabouts was a mystery.

Christie's manuscript consultant Jane Flower said it was the best archive seen in 30 years.

The collection, which is being sold by Conan Doyle's distant relatives, is likely to be broken up and sold abroad.