The British singer appears in the movie with RADIOHEAD stars Phil Selway and Jonny Greenwood as quirky musicians THE WYRD SISTERS, but his plans to commercially release music written for the film have been banned by Rowling.
An insider says, "Jarvis was really disappointed as he thought the songs were very good and wanted to release an album.
"He was upset as JK put her foot down and wouldn't allow it.
"She thought a group releasing CDs separately would confuse children."
Meanwhile, Potter producers Warner Bros are engaged in a fierce legal battle with a Canadian band, also called The Wyrd Sisters, over the use of their name.