There have been three series of Nebulous; the first was broadcast between 6 January and 10 February 2005. The series was well-received by critics, and a second series was broadcast between 5 April and 10 May 2006, with a third series commissioned by the BBC which began broadcasting on Thursday 15 May 2008 at 23.00 BST. The first series was released on compact disc on 5 February 2007 by BBC Audio.
The development of the series began with the production pilot episode, which was written by Graham Duff produced by Baby Cow Productions in March 2003. The episode, which eventually became "Night of the Vegetarians", featured much of the final cast, but with a number of changes: Rory was played by a different actor and Sir Ronald Rolands was voiced by Duff, while Gemini originally had two voices: a female voice played by Julia Dalkin, and a male voice by Nicholas Briggs. Nicholas Briggs had originally created a very deep, realistic soundscape, similar to those he had created for the Big Finish Productions Doctor Who audioplays, but was advised that "it's likely the listener will have distractions and will not listen to it more than once; therefore, the soundscape must be totally accessible from any point in the episode", toning down the sound effects to match the series' comic nature.
Nebulous is recorded in stereo at the Moat Studios in London, with every half-hour episode typically taking one day to record, including read-through and rehearsal. The sound is produced by Nicholas Briggs, using a combination of synthesised effects from a Roland SH-101 and foley sound effects. Audio editing is also carried out by Briggs, in order to bring the 30 minute episodes down to the 28 minutes mandated by the BBC to allow time for radio trailers between programmes.
The Earth's geography is also radically altered. A new mountain range was formed in Britain by a day-long ice age, and the Earth now has twelve and a half continents. Many locations have been displaced and reduced to islands, including Oxford University and the London borough of Deptford, which is now in the Indonesian Ocean as a part of the Cockney Islands. The solar system is equally altered: Jupiter has been deep fried by Harry Ramsden's, Mercury and Neptune have been knocked together, and there was an initiative to destroy the Moon, which according to the show was deleterious to the nightlight industry.
Religion also exists in the Nebulous universe. Pieced together following the Withering, theologians conclude that there were four true deities: the evil twins Yin and Yang, Feng Shui the destroyer, and merciful Bod, based on the children's television programme Bod; the theme tune of which has become a hymn, sung in Gregorian chant. Bod is analogous to God, hence the commonly-used phrase "Oh my Bod!"
Nebulous follows the adventures of the eco-troubleshooting team "K.E.N.T." (the Key Environmental Non-Judgemental Taskforce, named after the English county of Kent). The group is directed by Professor Nebulous toward the goal of restoring a natural balance to Earth. However, they are woefully under-funded; K.E.N.T. was forced to open a launderette to supplement funds. There is at least one other eco-troubleshooting team based in England, but despite their common goals they have a less-than-hospitable view of each other. L.O.U.G.H.B.O.R.O.U.G.H. (the Legitimate Organisation Undertaking General Humanitarian Business Operations Requiring Optimum Unconditional Global Harmony, named after the Leicestershire town Loughborough) is run by Professor Nebulous’ ex-love interest, Doctor Erica Flazenby. By comparison to K.E.N.T. it is over-funded and well-equipped, with bazers, black helicopters and info pills, which provide the user with information by ingestion.
Nebulous both parodies and pays homage to several well known science fiction programmes and films in both its setting and plotlines, often incorporating several different elements within a single story: Professor Nebulous himself is similar to Bernard Quatermass, a British scientist who lead a research group and fought aliens in the classic science fiction serial The Quatermass Experiment and its sequels. K.E.N.T. itself is based partly on the Department of Measurement of Scientific Work, nicknamed "Doomwatch", the eponymous organisation from the BBC science fiction television programme Doomwatch, and partly on the Doctor Who Organization "U.N.I.T", otherwise known as the "United Nations Intelligence Taskforce". The second episode of series one, "The Lovely Invasion", is a direct spoof of the Doctor Who episode "The Claws of Axos", while the "The Deptford Wives" takes both its name and premise from The Stepford Wives (and also borrows from Jurassic Park). From the first episode of series 3 onwards, this also began to include the recent Doctor Who spin-off Torchwood and the ITV series Primeval, with references to "baby dinosaurs falling through a hole in time" and "the sheer amount of paranormal activity in the Cardiff area alone ... starting to threaten the Earth's plausibility shield". Episode 6 of that series also parodied the tendency in British sci-fi for attempts to take over the world to start in Britain, with the chief villain (played by Tenth Doctor actor David Tennant) stating "Funnily enough, that's a tax thing", as well as one of the Ninth Doctor's nicknames, "the oncoming storm" (with Nebulous known as "the oncoming drizzle").
Following positive reviews and high listening figures, the second series was able to attract a number of guest appearances from well known actors, including Peter Davison, Steve Coogan, and Kate O'Mara. The third series will feature appearances from Julia Davis and David Tennant.
Reception to Nebulous was generally positive: a reviewer from The Times described the first series as "a winning blend of Doomwatch, Quatermass and British silliness that has cult written all over it", while the second series was described as "cool and cultish". However, The Daily Telegraph was more guarded, comparing the show to "Hitchhiker's without the philosophy or Red Dwarf without the energy", going on to say that show is "funny, but not seriously so". A reviewer for Doctor Who website UnitNews also initially expressed concerns about the level of jokes in the show, but later claimed "I should have been more patient because when they did arrive, coinciding with the introduction of the character Harry, they were relentlessly funny".