"Stay one day longer with me. They who go feel not the pain of parting; it is they who stay behind that suffer." --Henry Wadsworth Longfellow, "Michael Angelo: A Fragment" (1883)
The house belonging to Professor Lipton was also used in "Midsomer Murders." It was used as the Farmer House in "The Sicilian Defence" (S15E05), filmed approximately 7 months before this Lewis episode.
Three of the guest stars have starred as policemen in their own series: David Soul (Starsky & Hutch), Jason Durr (Heartbeat), and David Cader (Star Cops).
Lewis and Hathaway are descending the stairs from Dr. Yelland's room. The portrait hanging on the wall of the stairway landing is the same painting used to represent the late Lord Engleton in the "Swords into Ploughshares" episode of the "Rosemary & Thyme" series.
In some versions of "Lewis"--other than the original ITV UK broadcast versions, e.g., those available on Amazon video--Alan Cumming introduces the episode.