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James Nesbitt admits he felt anxious about playing the role of a British soldier for the first time in his long and varied career.

"This is the first soldier I've played since I was starting out as a young extra aged 16 or 17, and it was quite daunting," he explains.

"I said to the director Nick Murphy early on: 'I am worried about being believable'. I just couldn't picture myself. I kept telling him to keep an eye on my military bearing and my authority."

Once the production got under way, however, his worries quickly disappeared.

"A couple of things happened. First, Nick said to me: 'Don't worry too much, soldiers are human beings too'. It was really helpful, and I realised I was thinking about myself as an actor, rather than an actor playing a soldier," he says.

More significantly, Nesbitt found that the moment he put on the uniform and joined Occupation's fictional unit with colleagues Stephen Graham and Warren Brown, he began to behave as a soldier might.

"You put on the uniform, trust yourself and the character and it begins to fall into place," he says.

Many of the military scenes were filmed early on in the production. Nesbitt and his co-stars, Brown and Graham, found themselves forming a tight-knit unit.

"We tried to keep in character. So they were very much my team, my unit, my responsibility."

Nesbitt jumped at the chance of playing Mike, a military veteran approaching the end of his career in the Army who finds his life unravelling when he returns from Iraq.

"The one thing that the certain amount of success I've had has afforded me is the ability to be choosy about scripts. I thought Occupation was something I could be challenged by and the writing by Peter Bowker was exceptional," he says.

He was also drawn to the prospect of appearing in what is the ´óÏó´«Ã½'s first major drama on the Iraq war.

"I thought it was exciting to be involved in something which, while not necessarily ignored, has been hard for people to know what to do about, as a subject," he explains.

Mike, a long-serving soldier drawing to the end of his military career, is transformed by his experience in Iraq. So, too, are his colleagues, Danny and Hibbs.

"He has served in the Balkans and Northern Ireland, he is in his late thirties, he's been around a long time and he's coming towards the end of his time," he explains.

"In the opening scene, something happens to all of them and, from that moment, we plot their various paths and how they are interwoven – how that can separate them, how it can break them as a unit, how they find love, lose love and how their worlds are shattered."

He admits he found the process of playing a military man, exposed to the horrors and chaos of war, an eye-opening experience.

"One of the difficult things for us was to try and imagine what it must be like. It's impossible for us to imagine the things they see, the things they do, the impact it has on their lives when they leave their friends and families. The duality of their existence is extremely stark," he says.

"I wasn't surprised to discover that the marriage breakdown rate among soldiers who return from Iraq is something like 70%. Who do you share those extreme experiences with and how could your partner ever understand? In a way you need to get away from your Army colleagues, but who do you share those inner demons with if not them? Who lives those horrors with you?"

Nesbitt is honest about his attitude to the Iraq war. "I marched against it," he says. Occupation hasn't changed his opinion of the conflict. What it has changed, however, is his feelings towards the men – and women – who wear the military green.

"What has been extraordinary to me and all those involved in Occupation, irrespective of our own political persuasions or ideologies, is that we have come away from it with an enormous amount of respect for what they do," he explains.

"The discipline and the commitment of these men doing this job is quite extraordinary and quite moving."