Looking for a British or American film aired in Italy in the 1980s, set in early 1900s London

Hi everyone! I've been trying to identify a film I saw on Italian public TV in the 1980s. I believe it was a British (or possibly American) movie from the 1960s or 1970s. Here's what I remember: It was in color. Set in London, probably in the early 1900s (Edwardian-era costumes). It followed multiple characters who lived in one or more neighboring houses—fairly wealthy or upper-middle-class people. There was a shared garden, and possibly a greenhouse. Each character had secrets and personal intrigues they were hiding from the others. The story was mostly told through the eyes of a young writer, who quietly observed everything from his study window and understood the hidden connections. Eventually, the writer creates a play based on what he saw. At the end of the film, all the characters attend the play, and slowly realize that it's about them. I clearly remember a final sequence with the characters running up and down the stairs of a house. There was also an older character who wanted to reveal everything, but he had a speech tic or stuttered whenever it was about to rain. Does this ring a bell to anyone? I would really appreciate any help identifying this film. Thank you!