Shirley Cain (Miss Rossiter) also played Miss Climpson in the Lord Peter Wimsey mystery 'Strong Poison' from the series A Dorothy L. Sayers Mystery (1987).
Author Dorothy L. Sayers was very familiar with the advertising agency setting as she had herself been employed as a copywriter from 1922 to 1931. She worked on such accounts as Colman's Mustard and Guinness.
The secretaries place photos of movie stars in the typing room. The photograph on the filing cabinet behind Ms Parton is of Robert Montgomery who played Lord Peter Wimsey in Haunted Honeymoon (1940).