For Beatles fans across the world it has gained near mythical status. The 14-minute improvised track called 'Carnival of Light' was recorded in 1967 and played just once in public. It was never released because three of the Fab Four thought it too adventurous.
The track, a jumble of shrieks and psychedelic effects, is said to be as far from the melodic ballads that made Sir Paul McCartney famous as it is possible to imagine. But now McCartney has said that the public will have the chance to judge for themselves.