Flavia from "The Love Potion" is played by Mollie Sugden, who would later be best known for playing Mrs. Slocombe in Are You Being Served?.
YMMV for the 1971 film:
Adaptation Displacement: While the series is generally regarded as being superior to its film adaptation, the latter is generally more well-known to modern audiences, thanks to it getting a more widespread home video release and being repeated a little more often on TV.
One of the Christians imprisoned with Lurcio is played by Kenneth Cranham, who would later be best known for playing Harvey Moon in Shine on Harvey Moon.
Nero's girl is played by Carol Hawkins, who would later be best known for playing Sharon Eversleigh in The Fenn Street Gang.