You see, in America, it's quite standard for an actor to sign, at the beginning of a series, for five or seven years. The maximum any British agent will allow you to have over an actor is three years.
Julian FellowesWhat's difficult for American audiences is that they're used to a system here where you can get an actor for five years or even seven, and that is signed for at the audition. Whereas in England, no agent will give you an actor for more than three years.
Julian Fellowes