Defining Seasons
Since it's been a long time Thames Seasons has been aired it's a bit a detective work to find out which Episode belongs which Season. Thames Seasons haven't been reaired much and the net suffers majority of the Episodes. Here's guidelines to define Seasons:
Season 1 Extra 1
Season 1:
According the Best 1 the sets for the first Season looks most likely like this.
Season 2:
Set here from Episode 2 (of Season 2) looks like a cubic.
Season 3:
Set from Episode 5 (of Season 3) is red and there's a huge valve kind of thing in the middle of the set.
Season 4:
Set from Episode 1 (of Season 4) shows three TV pilars with metalic background.