To get straight in there, making a movie out of your book and being so involved with the process must have been a dream come true. How did you feel when you got the call that it was all going ahead?
It really didn't happen like that. It all started with Emma Watson, who had lots of meetings with heads to studios here in Hollywood. She was our champion, she really wanted to make it happen and it all started with her.
So you'd seen Emma as someone to play Sam from the beginning?
Yes definitely. It was when I saw her in Harry Potter and the Halfblood Prince actually. It was the scene where she was with Harry outside the common room and she's crying and it just broke my heart in that scene. I just thought she was fantastic and I noticed that every time I saw her in a movie, she just got better and better, and that was the first clue.
What brought it home to me was when I met her in New York in person, and I realised that I was fundamentally interested in this girl and she was fundamentally interested in me and my project. I knew how much she had to prove to herself beyond Hermione, that she could do all these other things and I knew that she needed to believe it, that she had the confidence to do it and I just had it. Watching her, I just knew.
Was it a similar feeling with Logan and Ezra or did they come along a lot later in the process?
With Logan and Ezra it was slightly different because they both auditioned whereas Emma didn't, but I still had a feeling about them when I cast them.
One thing we did notice about the film is that the tunnel song is different to the one in the book! Why did that happen?
You're right, we did change it. Well, when it came to actually flying through the tunnel, when you saw it, Landslide just wasn't energetic enough. To me, this is a triumphant moment, not a sad, somber one.
Did you try it with Landslide first?
We tried it with a lot of songs, but to me Heroes was just perfect. It's so terrific, so cathartic when Emma is up there flying in the truck. It just seemed to fit.
The music is clearly such a big theme in the book and Emma said that during filming she and Ezra formed a band with Logan, and he wrote them songs. Did you get to hear them?
I did. well, I heard them a little bit. I actually joined them a bit as I play guitar and I sing a little bit, so there was one time we all got together and played. Logan plays the piano, Emma sings and they let me join in, they were really living it being together. I mean, these guys, these young actors have so much pressure on them and on their lives. I can't imagine being 12 years old and having a multi-million dollar production weighing on my shoulders so this was a chance to cut loose.
It seems like they were a really tightly-knit group. So the friendship spilt over into real life?
Definitely. They are all lovely. You have to understand that when I was casting the movie, I was casting people, and it was very important to me that the people that were telling the story were kind and supportive and were nurturing of each other - and of me! Because I didn't want divas, that's not how I deal with things.
Not only were they good people, but each of them - for different reasons - had something to prove with this movie you know, and that's exciting. If you've got people on board that are hungry to prove something, there's nothing better, there really isn't. I look at it this way, like the way I look at rock bands. For the first couple of albums, they're on fire. They have so much to say and do, and that's how it is for them.
Well we definitely couldn't have thought of better people to play Charlie, Sam and Patrick – they are all individually so like how we imagined the characters in the book. If you were ever going to take one of their characters any further, whose would it be?
Well I'd like to write about all the characters but it would have to be Sam AND Charlie. You know, in different stages of their life, like working in an office or whatever. There are always certain people that stick out for you and ultimately the love story between Sam and Charlie is something that will always be there for me. I think it's the enduring story, them together.
Do you think it's something you might ever go back to?
I don't know, I might. I love the kids and it would be lovely to make another film with them. Maybe we should just get them all back together in ten years and tell another tale!