Theatre; Designated Mourner Cottesloe, London

"Oh, that Bernadette Shaw! what a chatterbox!" exclaims a queenie soldier in Privates on Parade. He should have met Wallace Shawn - a dramatist whose characters can talk all four legs off the proverbial donkey, not to mention the tail. There's a trio of them at it in the intercut monologues of The Designated Mourner, which - despite a hypnotic production from David Hare - I'm incapable of taking as seriously as it takes itself.

Guilt about being a member of a cosseted cultural elite on a planet where many people are oppressed and tortured is an abiding preoccupation of Shawn's. In this staging, privilege confronts you in the glowing shape of a great wall of golden ingots that stands behind the long, book-strewn trestle table where the cast sit looking out into the audience. In this latest piece, however, we're led to believe that an uprising of the underclass has violently altered the relationship between the elite and the masses. It emerges that, unlike his famous writer father-in-law (David de Keyser) and ex-wife (Miranda Richardson), who have been killed in the subsequent repression, Mike Nichols's Jack has survived into a world where "everyone on earth who could read John Donne was now dead".

The play is a gradual revelation of the inner cost of that survival. Expertly deploying a battery of mannerisms that increasingly grate - the tight, would-be winning, dead smile that clamps on to his face-lift; the merciless rascally chortle that bubbles determinedly under his words - Nichols shows you a man who adapts to the new Dark Ages by a wilful moral and cultural self-degrading.

But if he ends up literally shitting on books (an intriguing variation on Larkins's "Books are a load of crap"), The Designated Mourner suggests that Jack was always just a literary hanger-on rather than a true aficionado. Wanting to have it every which way, the play in effect says a plague on both your houses, for it also mocks and finds somewhat specious the patrician sensibility represented in Richardson's and De Keyser's highbrow, father- daughter mutual admiration society. It seems to me masochistically defeatist to posit a world where intellectuals are so powerless that they can be wiped out and where the most important thing to be said about the poetry of John Donne is that it can't save your neck.

But then, that world is left conveniently (defenders would say poetically) undetailed. The script has frequent recourse to the word "vague". Jack and his wife first meet in a "vague expensive clothing store": the old holders of office are called "a herd of swine whom we vaguely knew and would even vaguely nod to at cocktail parties"; and then, after the uprising, "there were to be some new people in high positions, some new policies, all very vague". A veritable epidemic of vagueness, it seems - but does this verbal habit of theirs put a precise finger on something wrong with these characters and their times, or does it let Wallace Shawn off the hook of having to imagine them and it more clearly? For me, I'm afraid, this play about the price of survival was itself something of an endurance test.