John Lennon mocks the deep thinking and hidden meanings attached to his work by Beatles fans and critics in a private letter, which is due to be auctioned next month.

"All my writing . . . has always been for laughs . . . I do it for me first . . . but it doesn't necessarily have to correspond to my thoughts about it OK?" Lennon writes in the two-page letter to an old schoolfriend, Stephen Bayley. 

"This goes for anybody's 'creations,' art, poetry, song etc. The mystery and that is built around all forms of art need smashing anyway." 

As an example, Lennon refers to the track "Being for the Benefit of Mr Kite," which is featured on the group's 1967 album Sergeant Pepper's Lonely Hearts Club Band. The psychedelic work has long been considered to be full of hidden meanings. Lennon confirms that the song was "taken almost word for word from an old theatrical poster." 

The letter is dated September 1, 1967, the day the Beatles recorded another psychedelic song, "I Am the Walrus." 

It is expected to fetch up to $36,000 at a rock memorabilia sale at Sotheby's on September 20. A suede jacket worn by Lennon in 1963 is expected to fetch up to $40,000.