The producers originally rejected director Alexander Mackendrick's choice of Katie Johnson for the role of Mrs. Wilberforce on the grounds that she might be too frail for the project, and so they cast a younger actress who died before filming began.
In an interview, Peter Sellers stated that this was "the first real film I made. I can remember all of that very well. I used to watch Sir Alec Guinness, who is an absolute idol of mine, do everything, his rehearsals, his scenes, everything. It was fascinating. Not that I could hope to be as good as Guinness. But he is my ideal, and my idol."
Because Katie Johnson (who played the old lady) was already 76 when she got the role, director Alexander Mackendrick went to the distributor and asked if her name could be prominently above the title, saying that this might be her last movie. The distributor agreed. Two years later, Johnson died. She only made one more movie.
Critics have praised William Rose's script as a first-rate example of British comedy and for doing an excellent job of capturing the world of British manners and tradition. Rose, in fact, was an American, who after World War II, had decided to stay and work in Britain, where he ended up also marrying a British woman, and so he was no stranger to British culture at the time.
As the parrot flies out of the living room and into the hallway, it clearly says "Alec Guinness" as it lands.