Perhaps owing to the location filming, although there are four episodes left in the series, this was actually the last episode of the original run of "Upstairs, Downstairs" ever filmed. Only Gordon Jackson was actually involved in the out-of-doors scenes filmed; the travel to Scotland by the other regulars is suggested by scenes filmed inside a car, coupled with exterior shots of a vehicle shot from a distance.
Mrs. Bridges expresses dismay at the thought of sleeping on the train to Scotland, saying that she hasn't done so since "the Tay Bridge Disaster, when I was a girl." The Tay Bridge Disaster occurred on December 28, 1879, when the first railway bridge over the Firth of Tay near Dundee, Scotland, collapsed during a storm as a train was crossing it, killing all aboard. The official death toll was 60, though up to 75 passengers may have been on the train. Conflicting contemporary reports blamed the engineering and the materials. Presumably, Mrs. Bridges is saying that news of the disaster inspired a lifelong precaution of not falling asleep on a train, lest something similar happen. The Tay Bridge Disaster occurred 49 years prior to the events depicted in this episode.
This episode takes place in May 1928.