It might be a pair of shoes or a jacket that helps Cillian Murphy get into character.

In the film Breakfast on Pluto, where he plays transvestite Kitten, he sported high heels and a blond wig. In Batman Begins he wore a terrifying hessian mask to play the villainous Scarecrow.

For his latest film, The Wind That Shakes the Barley, it's a flat cap and waistcoat.

Murphy, 30, plays Damien, an Irishman caught up in the rebellion against occupying British forces, the "Black and Tans." The Ken Loach film, which won the Palme D'Or at Cannes, spares little as it shines a light on the struggle that led to the 1920s Irish Civil War.

Murphy says it wasn't a conscious decision to star in an Irish film, but the chance to work with Brit Loach was irresistible. One of Loach's trademark techniques is to cast actors from the specific region in which his films are set.

Murphy is from Cork, the site of the film, and says the fact that the events happened only a few generations ago means they are "kind of my DNA."

"It made me go back and do a lot of research and uncover things that I hadn't been aware of."

He was taught the subject at school, but not to any depth: "The Civil War is not a very glorious time in our history."

While filming, Murphy stayed with his parents and was able to visit some of his favourite childhood haunts. He also learned about his own family history.

"Growing up, I knew that there had been a distant cousin of mine who had been shot and killed by the Black and Tans. And there was a plaque erected to him in the town of Cork. And then my dad told me that his father had also been shot at by the Tans. I think every family in Cork has some story or connection to these times."

Playing Damien was harrowing but Murphy, who ditched a career in law to follow acting, says it was rewarding.

"You either take a lot from it or you give a lot to it, but there's definitely an exchange. I love it when it's like that."

"You come home exhausted, but you feel like you've done a good day's work."