Starring roles for Rod Taylor and Cyril Cusack in this episode, which must have been filmed in summer 1979.
As far as I can tell the whole episode was filmed in the Cambridge area; many of the locations are quite recognisable even today. The Red Lion Hotel still exists and is near Whittlesford station. The final scenes are shot near Fulborn; it's distinctive windmill is clearly visible in the background.
The M11 western bypass wasn't yet finished when this was filmed, but further south the M11 was already in use.
Rod Taylor is perhaps most well known for 'The Time Machine' film, and for me, this episode's main interest is in glimpses of familiar locations forty years ago; this episode is its own time machine if you like.
The plot is pretty good and the acting is excellent. This makes it one of the better episodes in this series. Eight out of ten from me.