Writer/director Joe Cornish interviewed various kids in youth groups in order to find out what kind of weapons they would use if an alien invasion occurred.
The film-makers only used CG effects when absolutely necessary, and to enhance practical effects for the creatures rather than replace them completely. Even the smaller female alien that appears before the credits was a petite woman in a creature suit. A puppet-type head was used for some of the attack shots wherein Moses is suddenly bitten. The creature's head was a carefully constructed mask that had no eyes, and even the glowing mouthful of large, carnivorous teeth were achieved by animatronics (including twelve "servos") rather than added in post. The film-makers admit that it did help save money, but also had an unexpected benefit. The actors, rather than reacting to something that wasn't there, admitted that they were genuinely and unexpectedly frightened by the look and movements of creatures actually present (especially during chase sequences when a creature/creatures would pursue them at full speed). Nearly every actor said they felt especially intimidated-- many surprisingly so-- by the physical presence in a way they would not have if the creatures had been added digitally later. The same went for the majority of the settings; the director said it added authenticity and atmosphere to shoot on a set rather in front of a green screen.
Writer/director Joe Cornish was inspired to make this film after actually being mugged in real-life one night (much in the same way Sam was as portrayed in the film). He noticed his five young assailants were as scared as he was, and started researching their lives.
Most of the teenage actors were found through their schools and online open audition calls.
When doing research for the film, Joe Cornish asked one of the girls, "What would you think of this creature if you found it?" The girl said, "I wouldn't touch it, don't want to get chlamydia." That quote went straight into script; many lines were taken directly from research.
Writer/director Joe Cornish has stated that watching Signs (2002) and imagining what would happen if it took place in south London was an inspiration for Attack the Block.
Writer/director Joe Cornish had to remove fifteen pages of the script prior to the shooting of the film because of budgetary constraints.
Writer/director Joe Cornish grew up and lives in South London, where this film is set.
Joe Cornish was "very keen" that only Hi-Hatz used guns. "He's the genuine villain, the only villain. He's the only guy who shoots anyone. If I put guns in hands of other characters, it would become a whole different film."
Members of the gang compare the film's aliens to various fantastical creatures, all British in origin, namely: Dobby the house-elf from J.K. Rowling's series of Harry Potter novels; Gollum from the works of J.R.R. Tolkien; and Gremlins, who while they are now best-known for the two American films by Joe Dante, were born out of the imagination of RAF fighter pilots during World War II, and were initially popularized by author Roald Dahl in his first novel.
The areas and surrounding roads are named after well-known British science fiction authors: Wyndham Tower (John Wyndham); Moore Court (Alan Moore); Huxley Court (Aldous Huxley); Wells Court (H.G. Wells); Clarke Court (Arthur C. Clarke); Ballard Street (J.G. Ballard); Adams Street (Douglas Adams); Clayton Street and Clayton Estate (Jo Clayton); and Herbert Way (Frank Herbert). James Street may allude to horror writer M.R. James. Frank Herbert was, in fact, American; if the reference is supposed to be to a British writer, it may be another reference to H(erbert) G(eorge) Wells. Herbert Way is more likely a reference to James Herbert, the horror author who based most of his books in London.
Writer/director Joe Cornish did in depth research on language to accurately convey the way South London street kids speak.
Joe Cornish always had Boba Fett from Star Wars: Episode V - The Empire Strikes Back (1980) in mind when they did Pest's (Alex Esmail) costume, with his little rocket packs.
In the scene where the meteorite breaks open, a female alien cocoon is revealed. Director, Joe Cornish has expressed his wishes of keeping this prop as a back garden decoration.
Joe Cornish used mostly unknowns, kids who were involved in drama clubs or had otherwise demonstrated interest in acting. "1,500" young people were auditioned over and over, in part so Cornish would know the aspiring actors would show up on time and have self-discipline. During the process, they learned lines and did improv. After casting, the last two drafts Cornish wrote were influenced by the actors, letting them go through the dialogue and discuss any changes they wanted.
(at around 29 mins) The scene in which the police van smashes into the BMW was done in a single take.
Joe Cornish was inspired by the early, low-budget films of his favorite directors, like Steven Spielberg's Duel (1971) and James Cameron's The Terminator (1984). Directors who were "trying to make big movies even when they couldn't."
Franz Drameh, who plays Dennis, was originally under consideration for the role of Moses.
On filming a scene with five boys and five girls-all with dialogue- Joe Cornish watched a lot of Larry Clark films to figure out how Clark filmed scenes of teenagers chatting in such a naturalistic style.
The marijuana cigarettes several people smoke in this movie were actually made out of herbal tobacco.
Although the film is set in South London most of the location shooting was done in Islington, North London.
(at around 26 mins) The scene in which Alex Esmail throws fireworks underneath a police van took three takes to get right.
The film features over 100 effects shots which were completed over the course of 4 months by Swedish CGI outfit, Fido.
The knife that Moses(John Boyega) wields in the film is a Mikov 241 Predator, a rather rare and expensive switchblade knife from the Czech Republic. It is specifically the variant which features a modified bayonet grind, file-work, and premium RWL-34 steel. Similar knives were used in Casino Royale(2006) and Largo Winch(2008).
The film was shot largely on Heygate Estate in Walworth, Southwark, south London. The estate was demolished in 2014.
After a screening by Sony Pictures in Toronto to determine whether they should release the film in North America, Ron Sparks recommended they change its title to "Space Bears" or "Space Gremlins" to attract a larger audience.