When it came to casting it was a conscious decision not to cast well known actors as the leads. "We thought that it was more appropriate for the film that it should be not a star vehicle, rather it should be a community of people we cast as equals," says Boyle.
In the role of Jim, Boyle cast Cillian Murphy. Boyle had seen Murphy in Disco Pigs and thought he had a kind of innocence that he wanted for Jim. "The movement of his character from someone who is easy going, can just about be bothered to get up in the morning and clearly umbilically connected to his parents - the feeling of a child who is forced to become a man and by the end of the film be almost primal. I thought Cillian had that," says Boyle. Apart from the attraction of working with the creative team, Boyle, Macdonald and Garland, Murphy was very excited about the project. "The script was very different from anything I had read before and the character, Jim, is very physical. It's a big journey for the character, going from absolute bewilderment at the beginning and then this terrible vengeance at the end. "
Naomie Harris was cast as Selena. "When I read the script I really loved it. I thought it was brilliant and it stood out for me. Selena's character has survived the rage virus by being resourceful and independent. She has shut down emotionally in order to survive so it was quite a challenge," says Harris. "Naomie clearly had phenomenal ability and she is very able. She is rather elegant but very tough and clearly outstandingly capable for the part," says Boyle.
Boyle was very clear in his mind when he read the script that he wanted Brendan Gleeson to be Frank, the widowed father of Megan. "Having seen The General and all his other films I wanted this big, warm, beautiful man, this true father figure. You can feel the change in the film when Brendan comes on. His warmth and generosity comes out both on film and off. He is one of those guys you would have on every film if you could," says Boyle. For Gleeson the script was a real page-turner but not the kind of material he usually goes for. "I am not a great man for heading into the future really, or the past, but the fact that Danny was involved and the vibrancy of the script was a real pull. The part had a real warmth in this sandwich of horror and I just loved the part," says Gleeson. "Danny has this fantastic sensibility. It's a beautiful sensibility really and it's just been great working with him. "
Christopher Eccleston had already worked with Boyle twice before in Shallow Grave and most recently in Strumpet. Eccleston was cast as Major Henry West. "I had such a great time working with Chris on Strumpet," says Boyle. "He is developing constantly as an actor and I thought it would be very dynamic to get Chris to play Henry. He always brings humanity to stuff that he does and the idea of setting him that challenge for his character was very interesting particularly as we kept him as a public school officer. He makes you understand this man and what this man's take is on it. " Eccleston himself thought the script was terrifying and a real page-turner and particular liked the narrative. "My interest in playing one of the authorities is exploring the grey areas where authority figures are actually very necessary to us or even more humane than we are, rather than playing somebody who's just a forbidding, one-dimensional bully," says Eccleston. "Danny is very even-tempered and has a sort of ferocious personal energy of his own which tends to come out in his films. He creates a positive atmosphere, which everyone is comfortable with, and there is this tremendous verve with the way he uses his cameras and moves them. It's good to work with him again. "
Fifteen years old Megan Burns never thought she would get the part as Hannah, the quiet but confident daughter of Frank. "I tried to be myself in the audition but thought I had not got it as everyone was so different from me," says Burns. Boyle had seen Burns in Liam for which she won Best Actress at the Venice Film Festival last year but it was her audition that proved she was right for the part. "She just had incredible truthful quality about her which is really beautiful. A very simple, beautiful quality, very un-pushy - a kind of radiance which I loved about her," explains Boyle.
For Burn's part she had to lie on the ground under the cab while a mass of rats ran over her. "When I read the script about the rats I thought, no, they won't run over my face or anything and then on the day I realised I was wrong. I not only had to lie there but had to hold the rats on my face as they kept running away and Danny kept whispering 'Don't worry they're clean rats. They've all been shampooed this morning!'"
For the supporting soldiers' roles a talented group of young men were cast. Leo Bill as Jones, Ricci Harnett as Mitchell, Stuart McQuarrie as Farrell, Marvin Campbell as Mailer, Sanjay Rambaruth as Davis, Ray Panthaki as Bedford, Junior Laniyan as Bell and lastly Luke Mably as Clifton. Although they are in the film for a short period of time Boyle wanted audiences to identify with them all and see them as a community. "They are a great bunch of very exciting young prospects for future films," enthuses Boyle. "There are at least two potential movie stars in there. I daren't say which two of course!"
To prepare for their roles the soldiers, including Eccleston, were sent on a boot camp for the weekend. "I knew the rhythm and routine of the army would be valuable to them, to get it right so they looked and behaved like soldiers, and it worked really well," says Boyle. The actors attended lectures from ex-SAS soldiers and did military exercises. "We learned about the basic things of handling your rifle, making sure the rifle becomes part of you," Eccleston explains. "We fired off live rounds and I used both the machine gun and then a mounted machine gun, which to be honest I found pretty frightening. We didn't have a great deal of time but we packed a lot in learning a little bit how to move like a soldier and obviously how to think like a soldier". The camp also helped the actors feel like a unit. "Actors do that very easily anyway, you know, that's one of the great things about being an actor, you're used to chipping up somewhere and creating the camaraderie, and we did that very quickly", continues Eccleston. "I think in some ways it was good for those soldiers who came in and trained us, because actors are open, and they're willing to have a go and they can pick up skills quite quickly because that's what you have to do. And it's well cast and there's a good feeling among us. Hopefully what the soldiers will bring will be a different kind of humanity, different problems, and character problems. There's a lot that's decent in the men that we're portraying, we hope, rather than being just, you know, faceless authority. "
The final week of pre-production was set aside for rehearsals. Boyle used the time to take the actors out in the cab in London to go through scenes and to drive the cab. For Gleeson it was one of the highlights of the film. "It's such a blast. They're fabulous things. You can imagine how people could get very attached to them having it hanging around for 30 years just to look at it, never mind get into it. "