This episode was watched by 9.7 million viewers on its original transmission.
Notoriously, the excited seeming Dalek that dramatically launches itself forward after the bacterial emergency, was actually a goon (a stationary background prop) that was given a swift kick from behind by a stage hand to give it some life.
The Daleks look much better on location shots due to that part being filmed before they were sent on promotional events (check out Jo's very different hair) and having had their new paint job ruined by adoring children, they then filmed the rest of the story in the studio.
This episode takes place on Spiridon in the 26th Century.