The 44-year-old actor stars as Simon 'Sick Boy' Williamson in the sequel to the hit 1996 drama film.
"When we made the first movie, no one cared, right? No one knew who we were or what we were doing. (The sequel) was a little bit challenging because you've got people paying attention to you and it just sort of changes everything a little bit.
"You have to try to dodge people and try to lose photographers, and try and mask what you're doing because you don't want it ruined for everybody," Miller told People magazine.
"I always felt (a sequel) was a possibility. And I had faith in Danny Boyle, I really do. I know that he's not going to pull the trigger on something if it's not right.
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