Theatre: Private war: Paul Taylor reviews Alex Ferguson's The Flag at Bridge Lane

It would be hard to imagine pre-Holocaust scenes worse than those afforded by the trenches in the First World War - men dying with their guts hanging over their knees; escape tunnels where combatants clawed one another to death. But the Reverend John Calvin (Corin Redgrave), the left-wing vicar at the centre of The Flag, claims to have witnessed a bleaker spectacle. It was on the Embankment in August 1919, where he saw a collection of destitute, mutilated war veterans, shell- shocked, wrapped in newspapers, a shocking advertisement for that Land Fit for Heroes which they were promised.

Adapted by Alex Ferguson from a Robert Shaw novel, The Flag shows what happens when this vicar moves, with his family, from running a utopian (and failed) resettlement camp for ex-servicemen in North Wales to the living of a parish in Sussex, as the protege of Lady Cleeve, a widow turned on more by him than by his politics. It's 1926, and with the alarm caused by the General Strike, Calvin's hanging of the Red Flag in the church is far from appreciated by the local bigwigs. It's not the idealist vicar who suffers most from the reprisals, though, but one of his family.

Watching Redgrave's fluent, very well-acted production, you feel from quite early on that the material would have adapted best as a three-part TV drama series - the play is too pushed for time to avoid the impression of skimpiness. Take a character like Screever (Stewart Howson), who has the potential to raise some tricky moral questions. If he were a nasty piece of work before the war, does his experience in the trenches now justify his resumption of those old ways and even give him a convenient moral alibi for, say, terrorising brave ex-conchies with a knife?

Instead of presenting him on some such level of complexity, however, The Flag reduces Screever to a split-function melodramatic plot device: now a deep-dyed villain, now the poor man who, in the trenches, cradled the obscene remains of his beautiful friend. Until the ironic echo of that experience in the play's final moment, these two aspects of Screever are not brought into a revealing relation with one another.

The conclusion also evokes the image of Abraham and Isaac as they feature in the Wilfred Owen reworking of the story, which is recited when the destitute hijack a condescending church service put on for their benefit. Instead of slaughtering the Ram of Pride, Owen's Abraham, like some bitter personification of the war government, 'slew his son / And half the seed of Europe one by one'. But the parallel with Calvin feels forced, seeming the result of a bit of opportunistic plotting rather than the natural outcome of an idealist's neglect of family through preoccupation with his beliefs. Again, by pushing the problem to a melodramatic conclusion, the play evades the difficulties it throws up.

Oliver Milburn, Anna Clarkson and Richard Standing play the adolescents very finely indeed. But though the talent level in all departments is high, you may still wonder if the novel would have transferred better to the small screen than to the large stage.

To 2 April, Bridge Lane Theatre, London SW11 (Booking: 071-228 8828)