Russell T. Davies was commissioned by the BBC to write a 6 part serial to fill the opened up slot in Children's BBC in late 1991, when Tony Robinson decided to take a break from "Maid Marian and her Merry Men" and Russell T. Davies penned the first episode of "Dark Season" originally titled "The Adventuresome Three".
Russell T. Davie's 2008 "Doctor Who" Christmas Special, "The Next Doctor", recycles elements of the "Behemoth" in the "CyberKing". In both "Dark Season" and "The Next Doctor", the lead female villains are tricked into enthronement and entrapment inside a monster of their own making, which they accept as their destiny, but this leads to their downfall.
The "Doctor Who" production team originally sought to cast Kate Winslet as River Song in the revived series, as Kate Winslet had worked with Russell T. Davies on "Dark Season". The part went to Alex Kingston.
"Dark Season" contained some similarity to "Doctor Who", which Russell T. Davies revived in 2005. Most notably, Marcie occupies a similar narrative space to The Doctor, with Reet and Thomas as her companions. Nevertheless, the broad structural similarity to "Doctor Who" has been categorically denied by Russell T. Davies as intentional. Davies has claimed that the only direct reference to so-called "classic" "Doctor Who" is a scene in which Reet uses a yo-yo to test gravity.
Although the exterior of Eldritch's lair is actually the exterior of an old gas station, the interior was a set built on Stage 3A/B in what was, at that time, BBC's Ealing Film Studios. The set was built for three reasons: 1) The location used for the exterior was too unsafe for recording to take place inside. 2) The set of Eldritch's lair would be redressed as the interior of the underground bunker containing Behemoth. 3) The set (in it's Behemoth version) would have to be flooded it was safer and easier for the production to build the set into the water tank which is under the floor of the soundstage. By building in the water tank it gave them a three-level-high set.
Two weeks were spent at BBC Ealing Film Studios. The first week was devoted to all the scenes in the Eldritch lair and the second week for the Behemoth chamber. Some scenes in the Behemoth underground tunnels were actually recorded in the Robert Haining secondary school used for the school location, especially the large concrete steps Marcie and Thomas walk down, which later flood.