What can a play say about the horrors of the trench warfare of the First World War that we haven't heard a thousand times? Precious little – but Cameron Stewart’s lecture-cum-documentary-play My Grandfather’s Great War resonates on personal and contemporary levels that prove more than capable of refreshing the material.

Stewart’s grandfather, Capt Alexander ‘Tim’ Stewart, left behind a cache of letters and journals from the Somme, Passchendaele and several other important front-line battles. The material has been published in print and online, read by Stewart on BBC Radio 4, and adapted into this one-man show. Stewart plays both himself and his grandfather, switching frequently from enthusiastic biographer to square-shouldered, solemn, commanding soldier. Colder lighting, a few well-chosen sound effects and Captain Stewart’s verbatim testimony all combine to conjure up the muddy, hopeless wasteland of the front lines.

Early on, Capt Stewart is a solid, reassuring presence, but as the play progresses he becomes increasingly prone to violent outbursts. After we’ve become accustomed to his stillness, seeing him suddenly lunge wild-eyed at the front row of the Reading’s South Street Arts Centre wielding an imaginary pickaxe amply demonstrates the terrifying power of warfare to transform ordinary people into madmen. Unfortunately, as these frenetic episodes grow more frequent, their potency becomes greatly diluted. To his credit, even after many performances, the material still leaves Stewart breathless and choked with emotion. Throughout the show he exploits this personal connection to compare the very different mindsets of young men then and now.

From the diaries, Stewart teases a portrait of a generation that still felt able to trust the Government, many of whom made a conscious decision to fight even before conscription, and for whom patriotism was not synonymous with thickheadedness. Just because those convictions seem unthinkable to us now, says Stewart, doesn’t mean his grandfather’s generation were, as we often paint them, the innocent but ignorant victims of Government misdirection. And we thought we knew everything worth knowing about the Great War.

My Grandfather’s Great War is at Arlington Arts Centre, Newbury, on Thursday, March 19, and the Oxford Playhouse the following day.

Matt Boothman