Before Doctor Who's 2005 revival, Russell T Davies had developed an idea for an American-style science fiction/crime drama called Excalibur, inspired by Joss Whedon shows like Buffy the Vampire Slayer and Angel; the project was abandoned until BBC Three Controller Stuart Murphy invited Davies to create an after-watershed sci-fi series.

The word 'Torchwood' was originally used as a codename anagram of 'Doctor Who' to protect scripts from interception during filming of the 2005 series, and Davies later connected it to his shelved Excalibur concept to create the spin-off.

Publicity materials before the show's debut misleadingly featured Indira Varma as Suzie Costello among the regular cast, implying she would appear throughout the series, but her character was killed off at the end of the very first episode.

James Hawes, a Doctor Who director, was originally lined up to produce Torchwood but withdrew from the project before Richard Stokes took over producing series 1 and 2.

Russell T Davies was turned down by Fox for American financing of a future Torchwood series before eventually securing a deal with premium cable network Starz for the fourth series, Miracle Day.

Filming locations included RAF Caerwent near Chepstow for the military base scenes in 'Sleeper' and the booby-trapped warehouse scenes in 'Fragments', while the third series shifted production to real-life British intelligence headquarters Thames House in London.

The character Lois Habiba, played by Cush Jumbo, was written into Children of Earth specifically because Freema Agyeman was unavailable to reprise her Doctor Who role of Martha Jones.

The death of Ianto Jones in Children of Earth sparked the 'Save Ianto Jones' fan campaign, which raised over £10,000 for Children in Need, while also provoking abusive backlash against writer James Moran.