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.

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'm very fortunate that I get asked to do very different kinds of roles and I realize how much I enjoy that. I enjoy the challenge of transformation. There are actors who play one character, or a certain kind of character, the whole of their lives. I really relish the opportunity to have the challenge to totally transform.

I'm very interested in people, so if a character happens to be real, there's that much more to look at.

Somewhere the glamour has gone because of the industrialization of this whole process. I wish it [filming] felt as magical and glamorous as people want it to be, but it feels like a routine people are going through.

You're playing a character in a drama who happens to be based on someone who existed. It's never going to 'be' that person, but it's based on someone well-known, and you want to create enough of that person for it not to be a distraction.

I teach for the Book Trust, which promotes reading and writing with children.