For Firth, Mark's story really began to fall into place as the cameras rolled.
"For me, it was never simply a case of him being well-intentioned but naïve. I didn't want to see him behaving out of moral purity or idealism, I wanted it to be muddier than that," he says.
"Perhaps some of what he goes through is a product of a mid-life crisis, problems with his marriage or his wanting to run away from something he feels trapped by – perhaps any of those things might create disillusion or fear in a middle-aged man.
"But I think it's far more interesting to try to tell a story about a guy who has a multitude of motivations and conflicts and whose failings are very apparent.....more
