Hitchcock is a big ask. I am playing someone significantly older than me and someone significantly bigger than me. The stuff I find very interesting is why certain physical things have come about. How can he be light on his feet when he is so big? How can his weight vary so much? Where does this rather beautiful voice come from?

I've got to tell you, I've played real characters before and people always bring up this word 'impersonation,' and I'm never entirely sure what it means.

We're blessed with, as we were on 'Harry Potter,' lead actors who are amazingly grounded people.

I do always feel very proud and flattered by being asked to be a part of American productions playing American characters.

When you're training as an actor, a lot of the big work you're learning is to treat fictional characters like real people. You don't have the problem of discovering a backstory with real people, but there's always a mystery which is common to both fictional and factual characters. They are never quite the person you think they are.

They know you're not Alfred Hitchcock, but you need to be enough Alfred Hitchcock for them not to be bothered by it. That's a reassuring thing.

Often jobs are un-turndownable even before you read the script. You go, "Well, I have to do that."