In the First World War more than 290 soldiers of the British and Commonwealth armies were executed by firing squad, some for desertion and cowardice, two for simply sleeping at their posts. Many of these men we now know were suffering from shell-shock; they deserved treatment, not punishment.

Their fate, and a drive for them to be granted posthumous pardons, is the subject of an ongoing campaign. It is also an obvious subject for drama, but not, perhaps, for a children's book, which is how the script for Private Peaceful, which has just opened at the Trafalgar Studios, originated. (The book, by the Children's Laureate, Michael Morpurgo, has been glowingly reviewed.)

The story is about just one of these soldiers, Private Tommo Peaceful, aged 16. (He lied about his age to join up.) His life snakes through time like the trenches snaked the fields of the Somme.

Alexander Campbell, who is Tommo in this one-man show does, as far as it goes, a fantastic job. In the main, he performs the trick of playing multiple, believable, characters so well that the audience feels there was a cast much bigger than the actual number — one.

But, there are problems with the script, which seem to originate with the nature of its source. This is an excellent story, played superbly well, but seemingly for an audience younger than its main character. They may get a lot from it, but their adult companions may find rather less to satisfy.

What I found most difficult to accept was the idea that this young man, who should have the future at his feet but is instead facing death within hours, could be so happy, and not bitter, at his own needless fate.

The joyous nostalgia that prevails through most of the play does provide some touching and almost Rupert Bear-like moments, however, reminding us of a time when man's flight was romantic, when military pageants were human, and generals had handle-bar mustachios. And the background story of the bond within a loving family, brothers and sisters, and the quiet love of an innocent time, are pleasing in that gentle nostalgic way.

What lets the play down are those fights in the playground where Tommo was flying across the schoolyard with a bloody nose, and the rapid moments of conversation where the audience momentarily lost whether Campbell was playing Peaceful or another character.

But there are some spectacular moments: the old witch with the crooked finger, and Tommo's mighty retort in the trenches ("I ain'’t no chicken"”), the solemn celebration of his brother's greatest day ("No bells rung, no hymns sung"”).

So, when death does ultimately come, from a single bullet on 25th June 1916, it is a real death, of a real person, a person to which the audience feels connected.

The focus on the individuals involved in war, their feelings and fates, reminds us, if we need reminding today, that war makes pawns of us all. In the 90 years since Tommo Peaceful was put to death that, at least, has changed not at all.

Private Peaceful we salute you.

By Jon Grant