It is based on McGartland's recollections of being recruited as a teenager to infiltrate the Irish Republican Army for the purpose of collecting information for the British police from 1987 to 1991. He was kidnapped after his identity was discovered, but managed to escape and is still living in hiding.
"The film is not a true account of my story as it puts me at the scene of torture and murders," McGartland told the BBC. "I insisted on a new voice-over and a disclaimer at the beginning saying it the film was inspired by my book rather than being a true story."
The BBC said the author threatened to sue the filmmakers, but dropped the matter after reaching a settlement.
McGartland also said he disapproved of star McGowan's statement at the film fest that she would have joined the IRA if she lived in Belfast during the era the film takes place.
"It's easy to say this sort of thing when you live in LA," the BBC quoted McGartland as saying. "Rose McGowan's comments were insulting to victims of IRA terrorism and she should apologize."