Long-lost personal papers of Sir Arthur Conan Doyle which provide an insight into his private life are to be auctioned 40 years after they went missing.

The 3,000 personal letters, notes and handwritten manuscripts contain an acknowledgement that he had begun a relationship with Jean Leckie, who was to become his second wife, before the death of his ailing first wife.

The bundle also includes his initial outline for the first Sherlock Holmes novel, A Study in Scarlet.

Experts at the London auction house Christie's said that the collection - expected to fetch a total of £2m - also includes frank correspondence with his family.

The papers were taken from Conan Doyle's desk after his death in 1930 and stored at the premises of a London lawyer, where they remained until this year.

The collection also includes correspondence about his relationship with Leckie, and literary notebooks and letters from figures such as Winston Churchill and Oscar Wilde. It is on display at Christie's from today and will be sold on May 19.