The episode is the first to be released under the label Red Mirror, the result of Brooker experimenting with supernatural horror and past settings.

The episode received seven nominations at the 2024 British Academy Television Awards, winning Best Writing: Drama for Booker and Ali, and Best Photography and Lighting Design: Fiction for Stephan Pehrsson.

While selling shoes, she fantasises about hurting her xenophobic coworker, Vicky (Katherine Rose Morley), and an unsettling customer, Keith Holligan (Nicholas Burns), who killed his wife.

Nida is alienated by the Conservative, anti-immigration politician Michael Smart and vandals who paint the fascist National Front symbol on her door.

Forced to eat her biryani in the basement after Vicky complains, Nida pricks her finger on a drawer handle and bleeds over a bone talisman.

Gaap shows Nida a premonition: Smart becomes Prime Minister in an upset victory as leader of the ultra-nationalist Britannia Party.

[15] Brooker noted that, since Black Mirror's 2011 debut, dystopian sci-fi with technological themes had gone from rare to common, so he aimed to write horror fiction and period dramas.

[11] The episode was instead included in series six of Black Mirror, which Brooker described as a "conscious decision to slightly upend what the show is".

[19][20] Vasan is one of the few actors to appear in multiple Black Mirror episodes; she had a small role in "Nosedive", wearing silver paint and credited as "Space Cop".

[13][21] Her other roles include Amina in We Are Lady Parts (2021–) and Stella in A Streetcar Named Desire, characters that are underestimated, like Nida.

Kramer said that much research was done on 1970s department stores; the furniture and fixtures were made specifically for the episode and the colour palette was chosen to match the period.

[27] NVIZ Studio worked on the news reports that show Smart's rise to fascist leader, with iterations of Britannia Party messaging over three decades.

[31] Brooker said that while listening to a playlist he made of late 1970s music he recalled the "strong visual look" of Boney M. and based Gaap's appearance on Farrell.

[21] Essiedu saw the ending as "quite hopeful", choosing to show Nida and Gaap leaving Earth rather than the reality of spending forever together.

In The Independent, Nick Hilton classified it as the most comedic episode of the sixth series through the "mismatched partnership" of Nida and Gaap, with a similar combination of comedy, violence and apocalypse to The Cabin in the Woods (2011).

[38] Reviewers commented that the episode would fit in classic or contemporary anthology series such as Tales from the Darkside (1983–1988) or Guillermo del Toro's Cabinet of Curiosities (2022).

[39][40] However, Time's Judy Berman wrote that it shares "a shift in reality" that contains social commentary and "ends in a monster twist" with other Black Mirror episodes.

[39] Jen Chaney of Vulture commented that the "futuristic terror" was nuclear war or the racist Tipley characters' fears of white people being outnumbered.

[19][36] "Demon 79" is set during the 1979 United Kingdom general election that led to Conservative Margaret Thatcher becoming prime minister.

[16] As foreshadowing, Nida discovers old newspaper headlines describing a series of murders and a May Day celebration—this implies that Possett, the department store founder, previously used the talisman.

The latter signifies that Nida "has shed her meek demeanor and is ready to kill", according to Den of Geek's Brynna Arens, as the lyrics inform the listener that "Ma Baker is the FBI's most wanted woman".

[46] In the same scene, Nida steals a red leather jacket: Vasan said its "explosive pop of colour" contrasts with the many shades of brown in the shoe department.

Within both works, the main character discovers that a right-wing politician is set to become the leader of their country and commit terrible acts.

[49] Nida's aim—to kill three people to save many—was seen as an example of the trolley problem thought experiment by Screen Rant's Greg MacArthur.

[51] Vulture's Ben Rosenstock thought they had "great chemistry" and The New York Observer's Laura Babiak called them the "most watchable pair" of the series.

[54] Den of Geek's Louisa Mellor compared Gaap to the angel Clarence Odbody in the film It's a Wonderful Life (1946).

[19] Amy West, reviewing for GamesRadar+, said that Gaap's "deliciously camp flair" was aided by "one of the most fabulously flamboyant costumes" in the programme.

[55] Emily Baker of i positively reviewed the "hilarious delivery and ostentatious clobber" of Essiedu,[43] while Variety's Daniel D'Addario commented that Gaap is charismatic.

[35] D'Addario praised her "wide-eyed gumption" and Vasan's ability to "think through, onscreen", the ethical quandaries and limits of what Nida is capable of.

[52] On the other hand, Esquire's Brady Langmann criticised the ending as "puzzling" and Vulture's Charles Bramesco described it as a "cop-out whimper" that "undercuts the moral scale-tapping preceding it".