What a masochistic pleasure to see the middle classes losing their cool, abandoning all pretence at manners and revealing their nasty, troubled selves.

Yasmina Reza’s God Of Carnage, elegantly translated by Christopher Hampton, offers a funny, 90-minute exposure of this hypocritical process, of the fall from phoney grace to disgrace.

Reza, who made her name with the smash hit Art, enjoys reminding us of how apparently trivial incidents have a way of assuming brutal significance. In God Of Carnage a fight between 11-year-old boys that leaves one of them with two broken teeth and an “infected nerve” brings their respectable parents, the Vallons and Reilles, to a peace meeting that soon erupts in open warfare. Home truths hit home. The dividing line between civilisation and brutality, Reza asserts, remains permanently thin.

Mark Thompson’s expressionistic set gives a dramatic hint of the trouble to come by painting the Vallons’ living-room in rage-red, from floor to ceiling, with a decorative, engraved panel the same, almost bloody colour. Reza paints her characters, too, in the revealing light of satire as she makes deft mockery of their flawed morals and hypocritical manners, while director Matthew Warchus neatly emphasises the comic element. It is Ferdinand, son of Ralph Fiennes’s haughty corporation lawyer, Alain Reille, and his wife, Tasmin’s Greig’s effective Annette — someone big in “wealth-management” — who has inflicted the damage. It is the Vallons — Janet McTeer’s arty, handsome Veronique whose latest project is to wring consciences over the suffering in Darfur and her husband, Ken Stott’s banal, hamster-loathing domestic goods’ salesman — who dispense hospitality and convey polite hopes of an apology. What apology, though, can there be with Alain on hand?

Fiennes’s hypnotically unpleasant Alain, a languidly outspoken man who believes in a god of carnage and life as a rough-house, casts a worldly, supercilious air over the couples’ meeting. Thanks to this actor’s clever, beautifully pitched, black comedy performance Alain emerges as the sort of morally superior, unconcerned husband who incite wives to contemplate murder.

When not engaged on his mobile, brazenly bolstering the worried pharmaceutical company whose latest drug sounds fit only to be withdrawn, Alain cheerfully categorises his son as a savage true to a Boy’s Own tradition of murderous amorality, nonchalantly observes his nervous, liberally puking wife and slanders the Vallons’ marriage. The polite facades fall. Reza wants us to understand why the long-suppressed resentments of McTeer’s cooing but furious Veronique and Greig’s neurotic Annette flare up in comic-pathetic abandon.

An electricity power failure severely reduced the stage lighting and finally brought the production to a halt for a 10-minute pause. For the last half hour the actors were required to perform in semi-shadow, but it did not dim the confidence or the power of their performances. I finally felt, though, that the fracas over the schoolboy fight did not convincingly precipitate the play’s violent dramatics or confirm its belief in human selfishness. God Of Carnage doesn’t stimulate much thought, but it certainly provokes rueful laughter.