For the London scenes, police would close the roads at 4am, and filming would begin immediately. After 1 hour, the police would reopen the roads. The producers correctly predicted that asking drivers (including clubbers headed home) to either wait for up to an hour or find another route might make some of them angry. They got several extremely attractive young women (including Danny Boyle's daughter) to make the necessary requests, and the drivers responded quite amicably to them.
Danny Boyle and Naomie Harris developed a back-story to explain Selena's hard-nosed, ruthlessly pragmatic outlook. Apparently, Selena was forced to kill her infected mother and father to save her baby brother, only to discover that her brother was also infected.
Another aspect of rendering the zombie movie more contemporary was the idea that the virus didn't necessarily affect people physically (it doesn't kill them as in traditional zombie movies), but psychologically. Both Alex Garland and Danny Boyle felt that the idea that the virus renders people zombie-like due to uncontrollable rage was a good metaphor for the contemporary phenomenon of social rage (such as road rage, air rage, hospital rage etc). They liked the idea that the virus simply amplifies something already in each and every man and woman, rather than turning them into something entirely Other, as is the traditional route in zombie movies.
The shot of the notice board at Piccadilly Circus, with the missing persons fliers, caused some controversy when the film was first released. Some said it was insensitive to what happened in New York after the 9/11 attacks. The film was shot prior to 9/11/01, although it was released afterward. Danny Boyle said he based the shot on a photograph he saw from an earthquake in China. He also said that if he'd made the movie after the 9/11 attacks, he wouldn't have shot that scene.
For the scenes on the motorway, the production got permission to shoot on the M1 on a Sunday morning between 7.00am and 9.00am. The police gradually slowed traffic in both directions. Using 10 cameras, the filmmakers managed to capture a total of one minute of usable footage.
While filming the mansion scenes, the crew spent a lot of time at the Wooden Spoon in Downton, Wiltshire. They liked it so much that they gave the pub one of the dead bodies from the execution pile. The pub now has new owners.
The 'design' for the symptoms of Rage was based on Ebola, which is communicable in all primates (including humans), and is transmitted through the blood. Ebola is a hemorrhagic fever which leads to a rash, red eyes and both internal and external bleeding. Indeed, in 28 Days Later: The Aftermath (a graphic novel set between 28 Days Later and 28 Weeks Later (2007), it is explained that the Ebola virus was being used by the scientists as a carrier for the inhibitor which mutated into Rage.
Alex Garland and Danny Boyle did a great deal of research into social unrest, drawing ideas from things that had happened in Rwanda and Sierra Leone (such as the piling of bodies inside churches), but drew the line at using any actual footage from such incidents in the opening montage. All footage featuring dead bodies/desecration of bodies was faked.
Alex Garland and Danny Boyle felt that the notion of the living dead wanting to eat peoples' brains was outdated. One of the original factors behind zombie movies was a fear of nuclear power and its possible effects on people. Garland and Boyle concluded that one of the biggest fears in modern society is fear of disease, especially a viral apocalypse, such as Ebola or Marburg. Garland and Boyle were specifically inspired by such incidents as anthrax and bio-terrorism scares in London and the spread of mad cow disease and foot-and-mouth disease in the UK.
The decision to film on DV (using Canon XL1 cameras) was both an aesthetic and a logistic choice. Aesthetically, Danny Boyle felt that the harshness of the DV imagery suited the post-apocalyptic urban landscape and the grittiness of the film in general. In the production notes, Boyle says "the general idea was to try and shoot as though we were survivors too." Logistically, producer Andrew Macdonald claims that shooting with standard cameras, especially some exterior scenes, would've been impossible. As MacDonald points out in the production notes, "The police and the local authorities were quite happy to assist us because we could set up scenes so quickly. We could literally be ready to shoot with a six-camera set-up within minutes - something we would not realistically have been able to do if shooting under the restrictions of 35mm which takes a good deal more time to set up a single shot."
The hospital in the film is a real day hospital, open only during the week. The trust managers of the hospital hire out the building to filmmakers for weekends, and the productions pay the hospital directly, meaning the money from filming goes directly to the hospital's trust fund.
The Bible verse on Jim's postcard is from the Book of Nahum. Nahum was a prophet who predicted the destruction of the great city of Nineveh, the capital of the Assyrian empire. It was to be utterly destroyed as a punishment for its inhabitants' sins.
All of the mansion scenes that involved upstairs rooms were filmed downstairs because the mansion's owner lives upstairs. When Jim jumps through the window in the roof, he is actually jumping through a hole in the corridor upstairs down to the ground floor.
Athletes were cast as the Infected because of how important physicality is to them. Danny Boyle felt that since athletes can do things other people can't, they would be interesting when translated into the movements of the Infected.
The crew filed all of the necessary papers to destroy the Canary Wharf petrol station, but the police were (unintentionally) not notified. When the explosives were detonated, police sent fire brigades (although one was already present). Danny Boyle resolved the manner after several hours. The explosion cost £250,000 total.
Scriptwriter Alex Garland acknowledges several sources as inspiration for his screenplay, notably John Wyndham's The Day of the Triffids (1963), George A. Romero's "Dead" trilogy (Night, Dawn and Day) and The Omega Man (1971). Direct homages include Jim waking up in the hospital from The Day of the Triffids (1963), the chained infected being studied from Day of the Dead (1985), and the scene in the grocery store (people in the mall from Dawn of the Dead (1978)), the stop for supplies that saw a run-in with infected children (also Dawn of the Dead (1978)), and the military holing up against the plague with outsiders partially to deliberately include females (also Day of the Dead).
The single malt whisky that Frank is discussing with Jim in the supermarket is from the Lagavulin distillery. The whisky is part of the Classic Malts series and is known to be one of the smokiest and peatiest scotch whisky around. Frank appears to be a connoisseur considering his comments on the whisky when he says "peaty aftertaste" and "takes out the fire but leaves in the warmth".
The trivia items below may give away important plot points.
The execution pit scene near the end was filmed outside a church off Witherington Road, connecting Salisbury to Downton. One of the props teams didn't pick up the fake bodies after filming. A local hairdresser from Downton saw them from the road, panicked, crashed her car, and phoned the police, who came to investigate and interrogate the crew.
Prominently featured in the soldiers' mansion is a statue of Laocoon, the Trojan priest who attempted (in vain) to warn his countrymen that they had something to fear from the horse, just as Jim, Selena, and Hannah have something to fear from the soldiers.
In the end of the film, the pilot of the plane is speaking Finnish on the radio. The very last words he says are "lähetätkö helikopterin?" which means "will you send a helicopter?". According to this fact the survivors got rescued.
The scene when Major West reveals his plans for Hannah and Selena to Jim was written by Cillian Murphy, Christopher Eccleston and Alex Garland the night before it was shot. A different scene had been scripted and shot, but no one was happy with it, especially the two actors.
When Jim escapes from the two soldiers who are about to execute him, the shots of the jet flying overheard were shot by director Danny Boyle. During filming, Boyle took one of the Canon XL1's home, and spent 2 days filming planes through the trees in his backyard.
The film has engendered some confusion as to whether or not the virus is a worldwide phenomenon or whether it's confined to Britain. This is clarified on the DVD commentary however. When shooting began, Danny Boyle and Alex Garland intended to reveal that the virus had spread worldwide, which is why Selena mentions outbreaks in Paris and New York early in the movie. However, as filming progressed, they changed their minds and decided to render the spread of the virus more ambiguous. As such, they wrote the dialogue spoken by Sergeant Farrell (Stuart McQuarrie) when he is tied to the radiator as a counter-theory to Selena's claims, as he hypothesizes that Britain would have simply been quarantined at the first sign of trouble and that there was no way the virus could have reached America or mainland Europe. Obviously, the sequel 28 Weeks Later (2007) confirms that Farrell was entirely correct.
Danny Boyle explains on the DVD commentary that he shot all the scenes of the Infected in a particular style - using a type of slow motion feature on the Canon XL1 DV cameras with which the film was shot. Boyle explains that the cameras allow filming at up to 1600fps (normal speed is 24/25fps), but that shooting at such a high speed on a DV camera doesn't produce the same effect as it would on a 35mm camera. Shooting at that speed on a film camera gives basic slow motion, but doing so on a DV camera produces the kind of staccato effect seen in scenes involving the Infected. As Boyle explains it, it almost looks as if every third or fourth frame is trimmed insofar as the image has a 'jumpy' quality. Boyle also explains that during the climax of the film, as Jim runs around the mansion, all the scenes involving Cillian Murphy were shot in the same way - thus setting up for the audience a psychological parallel between Jim and the Infected.