The delineation between the actor and his part is a practical matter. When the camera runs, you want the actor to be the character.
Mike LeighThe reason my films work is because every actor on set is very secure. They're able to fly.
Mike LeighI can't negotiate and collaborate with a character to create a distilled dramatic investigation of the raw material. I need to work with an actor. That stuff about actors who stay in character all the time is nonsense.
Mike Leigh