The silver screen adaptation of Journey’s End is full of emotive performances in its portrayal of the trauma of war. Actor Paul Bettany tells Georgia Humphreys about creating an authentic adaptation of RC Sherriff’s celebrated play

Paul Bettany had one particular person on his mind while filming World War One drama Journey's End. His late Uncle Theo - a former army man himself - was man the actor based his portrayal of the wise and understanding Lieutenant Osborne on. "I loved him so very much," the 46-year-old declares ardently. "He was everything that was good about the stiff upper lip."

This "Britishness" is reflected on screen in a scene between Osborne and the young Second Lieutenant Raleigh (played by Asa Butterfield), a new arrival to the front who is heartbreakingly naive about the reality of what he is facing.

"He [Osborne] is totally able to put aside his coming demise, which he's certain of - he's taken off his rings and his watch - and just focuses on this kid [Raleigh], which is really moving, and it's practical and it's noble," explains Bettany. "Whenever I was in trouble, Uncle Theo always came at it in a loving yet practical way, and Osborne is like that - that's why I had him sort of darning, fixing things."

Set in March 1918, the adaptation of RC Sherriff's classic play (directed by Sal Dibb and with a screenplay by Simon Reade) follows the arrival of a group of British troops to the front-line trenches in northern France. Sam Claflin stars as the young Captain Stanhope (first played by Laurence Olivier on stage) who must lead C-Company with the ongoing fear that a German offensive is imminent, while self-medicating to deal with his own personal demons.

Of Sherriff's work, which he wrote in 1928 after returning from the war himself, Bettany says: "I can't think of an earlier piece that deals with PTSD."

Recalling how the film accurately depicts life in a dugout, Bettany reveals the cast filmed inside an actual bunker which was built by the crew. "It was quite something," elaborates the star, who made his name in British crime film Gangster No. 1. "You had to climb up to come down into it, and it's amazing how quickly you really felt like you were underground. It was very claustrophobic in there."

There's no denying portraying this very real period in our history feels a long way from Bettany's most famous roles, in the make-believe Marvel universe. He's known for voicing Jarvis in the Iron Man trilogy and playing the part of Vision in the Avengers movies and Captain America: Civil War. Earlier in his career, he dipped into rom-coms and also notably portrayed the albino killer monk in hit mystery thriller The Da Vinci Code.

Asked if he feels he lends himself well to period films, such as Journey's End, he says: "I don't know. I think that's for other people to decide. I know what you mean. I think some people have really modern faces - you see them in period things and you go, 'What? I don't buy it!' I don't know why."

And he seems unsure about whether he feels comfortable in the genre either. "I've never really thought about it. I love history." He pauses - something the contemplative star does numerous times while talking. "And I've always been fascinated by the First World War. So, I enjoyed the exploration of it."

Of course, there have been countless films made about the horrifying effect combat leaves on soldiers over the decades - the first adaptation of Journey's End was back in 1930. The power of the Oscar-nominated Dunkirk (albeit set in a different time period) is fresh in our minds, having hit cinemas last year.

Journey's End is a similarly heartfelt and action-packed piece, while also simply illustrating the boredom and ongoing tension the men felt during their days spent in the dark and narrow ditches. Interestingly, the film explores how food was often one of the only things they had to distract themselves with, something veterans who the cast spoke to "felt was relevant for them".

"I think the play feels modern in the way it's constructed and the things that people even talk about - food and stuff," says Bettany, who lives in New York with his wife, actress Jennifer Connelly, and their children. "So, I think on just a really human level, it's about the experience of war."

One challenge for Reade when taking on Sherriff's script though was not being slavish to the dated language: "The 'Tickety-boo' and 'Tally-ho, old chaps!' - they sort of tried to weed that out of the film," admits Bettany.

But it was also important to be authentic to the standout ideas and themes in the play, which led to Sherriff, a former surveyor, becoming one of the most prolific screenwriters in Hollywood.

For Bettany, who did a lot of reading about the First World War, it's the "sedentary nature" of it that's particularly interesting.

"Usually you can march towards or you can run away but you're just sitting there, and waiting for the bomb to land on you, really," he says. "I think there was something about that experience that turned people into writers."

Coinciding with the 100th anniversary of the end of the Great War, the film's release is definitively poignant. When it comes to more recent events in Europe, Bettany admits he found himself reflecting on the Britain we live in today during filming - he doesn't hesitate in describing Brexit as a "really bleak turn... It's hard for people to sort of understand the largess that they've lived under, actually. I think the prospect of a Europe that disintegrates is a terrifying one, I really do."

Journey's End is out in cinemas now.