"The character I play is a composite of everything that person has been through. He's interesting and recognisable.
"In this version he's an inhabitant of Edinburgh - as opposed to in the diaries, where he came from Windsor - so I play him Scots. I'm from that side of Scotland too so it gives me a rare opportunity to actually use a little bit of local colour in terms of the accent.
"He's shy and he's repressed, as much by the fact that homosexuality was the 'unspoken sin' around at the time, although his views on it are fairly forthright and direct.
"I think most people would respect him today. So that's quite interesting but he has many contradictions within him.
"One area of his life is his sexuality. His views are liberal because it accords with his feelings.
"In other areas they're far from that. He's by no means certain that Hitler was a bad thing, to put it mildly. In the course of the film these things come out in an understandable and human way.
"What's so wonderful about the writing and the realisation of what these people are like once you see them all together is that there is so much that was going on underneath the surface, while other things were happening on the outside.
"Our Hidden Lives is a perfect title really. I think some people's views are shocking and now, of course, quite rightly they're not expressed, but that doesn't mean to say they're not held privately.
"And what's shocking I think is to regularly remind ourselves that that is true. And although we wouldn't use those terms because they are politically incorrect, I think there are a number of people who just pay lip service to not being racist, for example.
"In the diaries, B comes over as a colossal snob. Now and again quite sympathetic but he's totally obsessed with his own notion of class, which is way below the level that he imagines it to be.
"People are always imagining that they are above things, that certain things are beneath them. That's very much his attitude."
