Therefore, its known narrative elements are not a part of the Doctor Who universe. It may have been the basis for a similar story in another medium, however — and that story may indeed be a part of the DWU.
The Dark Dimension, written by fan scholar Adrian Rigelsford, was a planned film commissioned by BBC Enterprises that was to have been released in 1993 to commemorate the thirtieth anniversary of Doctor Who.
Initial production Edit
The Dark Dimension (later known as Lost in the Dark Dimension) ran into obstacles which prevented it from being produced.
Some of the actors, particularly Jon Pertwee and Colin Baker, were not pleased that their roles were so small (the script featured the Fourth Doctor prominently while the others had small scenes). 
The main cancellation of the project fell to a miscalculation in the cost of the program. A large sum of money had not been added to both the cost and revenue of the project — that of the cost of putting the show on the air. When the calculations were corrected, it became clear that it was no longer viable to produce the film financially.
Attempts were made afterward to lighten the cost of the film by cutting key scenes and restructuring the film entirely - but these eventually fell through. Some minor elements of the scripts - such as characters not being able to be visible because of being in another level of time — were later used in the television story Dimensions in Time.
The story Edit
Far in the future of Earth, most humans have been wiped out. The Earth is left in ruins, the only people left on the planet being a resistance group which has been trying to hunt the creature that has done this to the planet. The group is searching an area, and their leader, Summerfield, suddenly finds a body. It is the Seventh Doctor — murdered by the creature. The Doctor is given a funeral which Summerfield finds fitting, as they are sent floating into sea and lit aflame. With the Doctor gone, Summerfield tells the others that they have to finish what the Doctor started on their own, attempting to send the creature who killed him into the time vortex to be destroyed. However, this would have instead sent him into Earth's distant past, where he would have plotted to change history.
The central idea to the story was that the creature -- disguised as the human scientist Hawkspur -- would have averted the events of TV Logopolis so that the Fourth Doctor would have survived his fall instead of regenerating. He also would have manipulated politics on Earth for the decades remaining, creating a world where he has ultimate power and a hoard of monsters.
The story would have centered on an older version of the Fourth Doctor, the Brigadier and Ace (all three from the timeline where the Fifth through Seventh Doctors never existed), with shorter appearances by the other surviving Doctors in minor roles, trying to defeat Hawkspur and set the universe right. Returning monsters would have included the Cybermen, Daleks, Ice Warriors and the Yeti.
The production would have also featured "Summerfield", who was written to potentially be an alternate version Seventh Doctor's companion Bernice Summerfield from the New Adventures book series if the audience interpreted it that way.
Furthermore Alistair Gordon Lethbridge-Stewart's son Alexander Stewart would have an appearance in the film. In the alternative timeline he would have been the boyfriend of Ace. In the restored timeline, Alexander would have died in 1979 at the age of ten.
The villain of the story was a creature "Entirely made out of chronal energy". In the beginning of the episode, the resistance group led by Summerfield would try to kill this creature by sending it into the time vortex, only for it to escape into the past, where it would possess Professor Hawkspur in 1936 and travel to the future to kill the Fourth Doctor on the Pharos Project. This story was to also feature almost all the classic monsters, with many of them being redesigned or feature totally new developments of the original design. In the original script, the story introduced a new type of Cyberman, the Cybercommander.
'The Cybermen were not like any we've ever seen before,' says Rigelsford. 'There was a specific Cyberman who was being made by the people at Henson's Creature Workshop. The guy who designed it was Chris Fitzgerald . It had holes in its knuckles and there was a point where it held up its hand, made a fist, and six-inch blades shot out of its knuckles! It was like Wolverine out of the X-Men comics; Cyberrine!'
The Daleks also were to have featured a redesign featuring a one-off new special weapons Dalek by BBC Workshop under Tony Harding supervision. A design of this "Special Weapons Dalek" was passed by BBC visual FX assistant Alan Marshall.
'The Daleks were going to have laser-guns that were going to be done with computer animation so the laser bolts would be in 3-D rather than just going 'Zap!' with a blue line. The bolts were going to be like spears coming out in 3-D.'
- Third Doctor - Jon Pertwee
- Fourth Doctor - Tom Baker
- Fifth Doctor - Peter Davison
- Sixth Doctor - Colin Baker
- Seventh Doctor - Sylvester McCoy
- Ace - Sophie Aldred
- Alistair Gordon Lethbridge-Stewart - Nicholas Courtney
- Alexander Stewart
- Prof. Oliver Hawkspur - Rik Mayall
Graeme Harper was scheduled to direct the story.
- "About three weeks worth of test filming was done including model and titles effects, and some location filming was also undertaken. 'We were going to go down to Shepperton film studios,' says Rigelsford, 'and have it shot on film on one of the largest sound-stages on Shepperton.'"
- Written by Adrian Rigelsford
- Director: Graeme Harper
- Producer: David Jackson
- Executive Producers:
- Penelope Mills
- Tony Greenwood
- Assistant Director: Kevan Van Thompson
- Script Editor: Joanna McCaul
- Production Manager: Nick Jagels
- Location Manager: Stanislaw Fus
- Costume Design: Bridget Tudor Evans
- Visual Effects Supervisor: Tony Harding
- Visual Effects Assistants:
- Video Effects Designer: Dave Chapman
- Post Production Effects: Kevin Jon Davies
- Special Effects Prosthetics: Chris Fitzgerald
- Title Sequence: William Latham
Further development Edit
Adrian Rigelsford wrote a book entitled The Making of the Dark Dimension which contained scripts and concept drawings. However, it repeatedly ran into release problems and has never been published. The Dark Dimension and its production were briefly mentioned in Rigelsford's own Classic Who: The Harper Classics.
- Short Synopsis taken from The Nth Doctor of The Dark Dimension
- NZDWFC - TSV 44: "Inside the Dark Dimension" by Jon Preddle