Directed by James Kent. Starring: Alicia Vikander, Kit Harington, Taron Egerton, Miranda Richardson, Dominic West, Emily Watson, Colin Morgan, Hayley Atwell. Certificate 12A; running time: 129 min.

Alicia Vikander isn’t British ? she’s the ravishing Swedish star of A Royal Affair, who acted her socks off as Kitty in Joe Wright’s Anna Karenina.

Once or twice, in her glorious performance as Vera Brittain in Testament of Youth, you can hear a telltale Scandinavian vowel drop. But you shouldn’t hold that against her. If all you wanted to talk about in Gone with the Wind was Vivien Leigh’s broad mimicry of an Atlanta accent, you’d be missing an awful lot, to focus on not very much. In Vikander’s case, it would be her thrillingly astute portrait of a young Oxford undergraduate whose ideals are beaten into shape ? bitterly forged, you might say ? by the heartbreak and gruelling trauma of the First World War.

The comparison between Brittain and Scarlett O’Hara might seem bizarre. But remember Atlanta’s makeshift hospital, the hundreds of war dead and wounded, and how transformative the experience of volunteer nursing was for cinema’s most famous Southern debutante. James Kent, the director of this careful, shaded and forthright adaptation, certainly sees a kinship, which is why, at Etaples, his film copies one of the most famous crane shots of all time, a slow God’s-eye sweep over the ranks of the dying.

In Brittain, he finds something of a Scarlett: single-minded, rebellious in her ambitions, and the object of many men’s covetous love, whether it’s her father (Dominic West), who resists Vera’s desire to sit the Oxford entrance exam; her hearty brother, Edward (Taron Egerton); or two of his most handsome contemporaries, Roland (Kit Harington) and Victor (Colin Morgan, a subtle standout), who quietly vie for her hand before they, like Edward, are shipped off to the Western Front.

At the beginning of the film, Vera would rather run away from the lot, seduced by dreaming spires and everything books might teach her. She has a flighty, sceptical intelligence. Vikander doesn’t guarantee herself our sympathies, but deliberately rebels against those, too: she’s great at capturing the flushed moments when Vera bottles her pride, refusing to be baited by the bluestocking tutor (Miranda Richardson) whose every eyebrow raise is a hasty assumption of frivolity.

What awaits Vera in the next four years, as anyone who has read her memoir will know, is an appalling catalogue of personal loss, a scalding of the soul. As a film , Testament of Youth glimmers with sadness, but also the apprehension of sadness: we know that not all of these boys will be coming back.

Conversations sputter into awkward silence, especially when Harington’s Roland comes home on leave, tormented by the haphazard brutality of trench life. He puts on a brave face with his peers, but can barely look Vera in the eye. Kent makes the many farewells as pregnant as they need to be, without milking them for forced melodrama. Avoiding the hectic ostentation which has marred many a Joe Wright project, his alternative is a restrained cinematic polish that feels wholly appropriate to its subject: it’s soberly moving.

The film’s exquisite costumes, by Consolata Boyle, and photography, by the increasingly indispensable Rob Hardy (The Invisible Woman) are much more than shop-window attractions. The most beautiful effect is the simplest, though: it’s when soldiers, some barely known to us, break the fourth wall, looking back at Vera in her mind’s eye, and back at us across the century since, inviting remembrance but implicitly urging something more.

Vera must combat consoling lies, empty words, the myth of painless and noble death. The truth is silence and agony. It’s rather wise of Kent and his screenwriter, Juliette Towhidi, to have subtracted virtually all of an author’s own words and still make her message ring out so powerfully ? to have found and visualised their deeper truth. They’ve done hugely stirring justice to Brittain’s life’s work, which was to deny every false meaning attached to battlefield death. As one of the great British pacifist thinkers, she admitted with an unflinching radicalism that the cruel culling of a generation meant nothing. This very fact was its meaning.