© Focus Features
The actor stars as female lead Emma's (Anne Hathaway) boyfriend, who finds himself unable to compete with her love for arrogant Dexter (Jim Sturgess).
Spall told The Guardian: "I read the script before I read the book, and as soon as I read it I thought, I want to play that character.
"Sometimes you go, 'I wish I was playing the main part', but not at all in this case. I really wanted to play Ian.
"My American agent afterwards was like, 'You know, Rafe? I'd love to see you play a winner'. But Ian's the kind of bloke I want to play; I think as English people, we like a loser."
Spall, 28, also defended the casting of Anne Hathaway in the role of Emma, who comes from Yorkshire.
"Everyone was like, 'Why is an American girl playing a girl from Yorkshire?' But I think Anne is a brilliant actress and Rachel Getting Married is genuinely one of my favourite films, so I was really excited to work with her," he said.
"She plays against her beauty successfully; she has a vulnerability and it is believable that she's still insecure. That's a clever thing to do. Also, she's a movie star, and it's fun to work with movie stars."
Spall will next be seen in Ridley Scott's Alien-inspired Prometheus with Michael Fassbender and Idris Elba.
Watch the One Day featurette below:
