The whirligig of time and politics has brought renewed and terrible relevance to Bernard Shaw's Saint Joan. No 20th century British play better demonstrates the dangers and intolerances of religious fundamentalism, its abiding threat to liberal ideas of individual freedom.

Some people may latch on to the idea that Joan, compared by Shaw with a Mahometan, ranks as religious martyr and fanatic, who dies because she heeds voices that command her to expel British troops from France. Such a sensational view of the Maid - as a thoroughly modern terrorist - does not explain the play's contemporary importance.

This is the heart of the matter. The trial scene, despite the ornamental extravagances of Marianne Elliott's production, marks one of the great, unequal contests in modern theatre.

Shaw pits Anne-Marie Duff's flayed, pathetic and heart-rending Joan, insistent on her direct line to God, against an Inquisitorial Catholic Church, for whom Oliver Ford Davies's frostily grand but over-rhetorical Inquisitor intones the rules of uniformity.

The Church denies the doomed girl any right to personal conscience. She must ignore the dangerous voices she hears. To do otherwise would make her a heretic and Protestant. Like Martin Luther, this woman in male warrior's armour believes to go against conscience is neither right nor safe. She struggles, centuries before Enlightenment, against the Church's discipline.

She dies for her religious individualism and in a brilliant stroke of theatrical invention Elliott makes the crucial point that religious intolerance remains alive and well today: the production ends by reprising the first scene's opening moments, as if to say Saint Joan's dilemma is ours.

Duff, whose Joan scales the risky heights of pathos and vaults her to the forefront of her acting generation, makes this battle of religious wills fascinating. Slight of physique, androgynous, and Irish accented she conveys Joan's fatal combination of intensity and ardour, assurance and vulnerability. No wonder she inspires Paul Ready's ridiculously down-market, queeny Dauphin and Christopher Colquhoun's dull Dunois.

After Angus Wright's superbly languid, drawling Earl of Warwick has condemned the Maid as an ideological threat to the English nobility, this Joan appears in the trial scene, dazzled by spotlights and surrounded by menacing clerics.

Her outbursts of fury and fear look painfully real.

The production itself, though, in Elliott's ponderous, mainly-modern dress and silver coffee pots rendition, irritatingly harks back to Sixties experimental theatre.

The first burst of Jocelyn Pook's music, in international bursts of World Chill - from Gregorian chant to Gaelic lament - introduces us to stylised, slow-motion actors.

These performers hand each other chairs to arrange around Rae Smith's square, mobile, elevated stage. They remain a distracting presence with their fussy chair arrangements, never more so than in Elliott's bathetic interpolation of an immolation scene.

Joan is strapped at the top of a pile of chairs, there to burn, to soulful musical lament. Yet the play itself stokes up a genuine theatrical blaze.