The story suffered from The BBC slashing the rest of the season's budget due to the economic crisis the UK was suffering, leaving them with barely enough money to build the spaceship set, and nothing to build sets of the caves, or to shoot them on location. As a result, they ended up having to resort to filming all the non-spaceship scenes on a bluescreen, and matte the actors into miniature cave sets.
One of the least popular Doctor Who (1963) stories, fans voted this the third worst story of the entire run in fan site Outpost Gallifrey's 40th anniversary poll in 2003.
Budget restrictions were so tight on Underworld that cancelling it altogether and allotting its budget to "The Invasion of Time" was suggested, but was ultimately rejected by Graham Williams.
This story was inspired by the story of Jason and the Argonauts.
Ankh was named for an Egyptian symbol for life, while Lakh is an Indian word for "one hundred thousand", referring to the timespan of the Minyans' search for the P7E. More modern figures were also referenced: Rask was named for nineteenth-century Danish philologist Ramus Rask, Tarn for nineteenth-century French poet Pauline Tarn (who wrote under the nom de plume Renée Vivien), and Klimt for early twentieth-century Austrian painter Gustav Klimt. Each of these had engaged in various works associated with ancient Greece. The Leibemann maser weapons were named for early twentieth-century German painter Max Liebermann.