The film is based on Robert Harris' book that gives an unflattering account of former British Prime Minister Tony Blair.
The story revolves around an unsuspecting writer who ghosts the autobiography of a former prime minister called Adam Lang. Miss Cattrall plays an aide to Lang who knows his innermost thoughts.
"I thought it was fascinating. It's knowing when you need to say something and when you need to leave the room," the Telegraph quoted her as saying.
She added: "I found it quite terrifying. Behind these political masks are these machinations and these evil people who are so egocentric and demonic. I found it more of an affirmation of something we know is going on, but don''t want to acknowledge because it's so frightening."
Roman Polanski has directed the film.