"Carnival of Light" -- a 14-minute experimental track recorded at the height of the Beatles' musical experimentations with psychedelia and inspired by avant-garde composers such as Karlheinz Stockhausen -- has long been considered too adventurous for mainstream audiences.
In an interview for BBC radio, McCartney said his bandmates and their producer George Martin had vetoed its inclusion on the exhaustive 1990s "Anthology" collection, according to UK's The Observer newspaper.
McCartney confirmed he still owned the master tapes, adding that he suspected "the time has come for it to get its moment," The Observer reported. "I like it because it's the Beatles free, going off piste," McCartney said.
Almost everything recorded by the Beatles from their early days in Liverpool and Hamburg to their break-up in 1970 has been released to meet insatiable public appetite for anything to do with the legendary Liverpool quartet.
In the 40 years since its recording, "Carnival of Light" has acquired near mythical status among Beatles fans who argue that the existence of the track provides evidence of the group's experimental ambitions beyond their commercially successfully pop career.
The improvised work features distorted electric guitars, discordant sound effects, a church organ and gargling interspersed with McCartney and John Lennon shouting random phrases like "Barcelona" and "Are you all right?"