Siobhan McKenna agreed to take the role for the opportunity to work with William Wyler, in spite of the fact that she was giving eight performances a week on Broadway in 'Saint Joan".
Paul Scofield was cast as Howard Joyce but had to back out when the film he was making was running over schedule, and Michael Rennie was hired as his replacement.
In John Mills' autobiography he writes that this was his first and last live play on TV. During the opening scene, shooting the blank cartridges were duds and there was no sound; and during a tense scene with Michael Rennie two cameras collided causing a large portrait of King George V on the wall behind them to fall to the floor creating a loud thud.
The original Broadway production of "The Letter" by W. Somerset Maugham opened at the Morosco Theater on September 26, 1927 and ran for 104 performances.