The idea of transformation - playing something I'm not - is the bit I enjoy most about acting.

I just like voicing films in general. I do a lot of documentary work and it's a short hop really to narrating a character, especially if you're on film and you're there in a visual way. It sounds obvious, but voicing an animation really focuses you on the way that you're communicating through your voice. It's a very specific ability that you need to be able to have in order to pitch it just right.

Interestingly, this character [Doctor Nash] is probably closer to me than somebody like the evil Sir Godfrey in Robin Hood or Lord Blackwood who wants to take over the world in Sherlock Holmes. This is a character that's English, he's based in London, and so it's closer to me than a lot of stuff I've been doing recently.

In the movie, you have to decide as an actor how you are going to give a character presence. You can't really move, walk, and talk like yourself. This creates something so you have to find something "other".

And I think in your 40s, you land a little bit, physically and mentally, you arrive at a place where you feel you've learned some stuff. Having children at that point meant I had something very useful to do for the next 20 years.

[Before I Go To Sleep] script was a great journey with all the twists and turns that were kind of unexpected. I had to finish the script, and I thought if we can emulate this in the film, it's going to be a really good film.

My mother moved abroad when I was 11, my dad wasn't around from the time that I was a baby, so I was not the product of a family, but a product of observation - of watching what went on around me, of watching who I liked, what I didn't like, what I thought was good behaviour and what I thought was bad behaviour and tailoring myself accordingly.