A private collection of letters from Sir Arthur Conan Doyle and Harry Houdini to a medium from the 1920s are expected to fetch thousands of pounds at auction in Kent.

The correspondence to retired marine officer and clairvoyant Capt John Bartlett shows the Sherlock Holmes’ author’s enthusiasm for spiritualism, and frustration with his peer and magician Harry Houdini’s scepticism.

A separate lot consisting of a letter from Houdini promising unspecified photographs to Capt Bartlett is dated June, 1920.

The notes are collectively expected to reach up to £6,500 at Canterbury Auction Galleries on Saturday.

In one letter Conan Doyle appears to disparage his one-time friend Harry Houdini.

Conan Doyle’s note reads: “Possibly his widely announced searching for spiritual proofs is also a cover.”

The author became involved in the spiritualism craze of the early 20th Century following the death of his son Kingsley in World War One and formed an unlikely friendship with Houdini over their shared belief in the afterlife.

However, their relationship soured over Houdini’s attempts to expose fakery among mediums.

Dave Parker, auctioneer from Canterbury Auction Galleries, said: “Houdini was a sceptic looking for more information while Conan Doyle was a militant believer.

“They went down the same path for a very short while and then they fell out badly about methods.

“Houdini was after uncovering fraud which there was a lot of at the time.”

The letters, whose seller wishes to remain anonymous, are expected to gain interest from US paranormal fans in particular, the auction house believes.

Mr Parker added: “We get lots of interest from around the world.

“Anything to do with spiritualism or the history of spiritualism is extremely popular.”