R C Sherriff’s Journey’s End was a smash hit from the start. Based on his time in the trenches, it’s a deft, funny and quietly devastating play. Sadly, the new film version by Saul Dibb is a damp squib, snuffing the life from Sherriff’s script. Saved only by an excellent cast and a superb performance by Paul Bettany, it’s let down by a director who makes all the wrong choices.

In March 1918, an infantry company led by the older-than-his-years Captain Stanhope returns to the front line, threatened by an imminent German advance. Raleigh, a fresh-faced new officer, has wangled his way into Stanhope’s company, having hero-worshipped him at school. But the war’s taken its toll, and Stanhope is held together only by duty and the bottle, and by the support of ‘Uncle’ Osborne, his second in command. As all hell breaks loose outside, a war of nerves explodes in the dugout.

Saul Dibb (Suite Francaise, The Duchess) is blessed with a brilliant cast. Sam Claflin (Hunger Games, Me Before You) is compelling as the troop’s leader who’s losing it. One of our best upcoming actors, Asa Butterfield (Ender’s Game, Hugo) catches the schoolboy, officer-class innocence of Raleigh, coming to terms with Stanhope’s strain. Toby Jones, as Mason the cook, and Stephen Graham as the ever-hungry Trotter, bring a nuanced blend of comedy and humanity. But it’s Paul Bettany (Master and Commander) as Osborne who makes the film worth watching, a fabulous evocation of decency under fire.

But visually, it all comes apart. Dibb dogs his characters with a camera so irritatingly close it’s like a trench-bound game of ‘What's The Time, Mr Wolf?’. Clearly intending to convey the claustrophobia of the setting, it’s a one-trick move; but Dibb does it time and again. Behind people’s ears, in their faces; and in a pointlessly extended shot he follows a pair of boots through unconvincingly shallow mud that doesn’t evoke Glastonbury, let alone the horrors of the Western Front.

Dibb’s dead-hand approach fails to trust his actors enough - except for Bettany, who’s the only one given room to breathe. Missing the beats that punctuate the play, the film rushes the jokes and banter, and undermines any sense of camaraderie-in-peril. Stanhope’s disintegration is skewed to the point of dramatic irrelevance – it could be any of us undergoing mental anguish. That’s contemporary, maybe. But it lacks the peculiar knife-edge battle of duty and despair of the 1914-1918 generation.

The demise of a character is telegraphed, sapping the surprise and the gut-punch force of it. Stanhope’s crisis of character is over-symbolised in the sloshing of whisky, no longer the secret soak of the play. You hear that Stanhope’s a great leader – but you don’t see it. That’s not Claflin’s fault, it’s a fine performance. But Dibb’s decided to focus on the decline, and there’s less drama there.

Like the wasteland of the landscape, the music by Hildur Gudnadottir (Arrival, Sicario) is deliberately muddy and indistinct; so much so that it’s a surprise over the end credits to see that it consists of several tracks, not one. It’s suitably atmospheric, though, and Dibb does at times ditch it for silence, to good effect.

Sherriff was a screenwriter too – penning Goodbye Mr Chips and the superbly understated The Dam Busters. Sadly, this version of Journey’s End is no sort of tribute to Sherriff’s play, nor to the tradition of deftly written films about war. It’s telling that the film concludes with a caption that millions died in the First World War. Really?

Well-intentioned, Journey’s End just about survives the stifling direction from Saul Dibb, thanks to a wonderfully committed cast. But, like life in Stanhope’s trench, only the sheer pleasure of Paul Bettany’s Osborne makes the film worth bearing.

The First World War is a strangely underrepresented event in cinema, usually reduced to an incidental moment, a footnote to add colour to a character. This is in stark contrast to cinematic representations of the Second World War (two of the Best Picture Oscar contenders focus on it), which feels explored far beyond there is any necessity to. 2018 marks the centenary of the end of the First World War, and so it feels right that a film like the powerful Journey's End should be released.

Based on R.C. Sheriff's famed 1928 play, the film follows new solider Raleigh, who uses his connections to sent to the front to join Captain Stanhope's battalion. He finds a broken man where once there was a school hero, as Stanhope and his soldiers await the coming German attack.

One of the assets of Journey's End is its strong central cast, with much of the narrative heavy lifting by the very good Sam Clarflin and a heartbreaking turn from Asa Butterfield. I didn't quite buy into the way Butterfield's character develops here, but that is not the fault of the talented young actor, and more the compressed timescale over which proceedings take place (just four days). There is also room in the ensemble for the exceedingly talented duo of Toby Jones and Steven Graham, who deftly balance the quieter, more dramatic moments with the much needed instances of comic relief. But the true standout here is Paul Bettany, who has never been better. His performance is just the right level of reserved without slipping into caricature, he is a warm presence throughout and, in the film's final third, the carrier of much the emotional burden that makes the final act so powerful.

Where the film stands apart is with Laurie Rose's dynamic cinematography and Hildur Guðnadóttir and Natalie Holt's ominous score. The camera prowls through the trenches, often lingering on an actor's face as we survey their response to the horrors of their situation. And the score is as terrifying and powerful as the one that stands out so distinctly in Dunkirk. It is its own beast, a constant reminder of the situation that this characters find themselves in, Together they make the film a claustrophobic, often horrific drama.

Director Saul Dibb marshals all these components into a compelling whole, intimate and razor focused. Though a handsomely presented film, Journey's End is never sentimental, building to an earth-shattering climax that is as devastating as it is expected. This is indeed an exceedingly good war film, one worth seeing for Bettany's exemplary performance alone.