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 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.
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.