Opera The Rise and Fall of the City of Mahagonny, ENO, London

Brecht was into boxing in a big way. Not personally, you understand ("You wouldn't hit a bloke in glasses, now, would you?"). But when it came to opera, Bert went at it with both gloves off. He just couldn't handle all that sensual indulgence and emotional surrender, all that avoidance of intellectual engagement and lemming-like suspension of disbelief. After all, this was a man who wore a black leather jacket and smoked a blunt cigar.

So when Brecht and Weill first teamed up, and tried their hand at the big opera project to come, they set their "little" Mahagonny Songspiel in a boxing ring, and had the cast march round at the end waving political placards about. It was a knock-out. Round 1 to Bert Brecht and his head- banging "Alienation Effekt" (just feel the weight of that krazy K).

After that, he was ready to take on all comers. And, of course, he couldn't lose. The A Effekt hands stage directors the ultimate critical double bind: hate the show, and the alienation's obviously working; love the show, and everybody's happy. A classic case of damned if you do, damned if you don't. And, by the end of three hours' emotional disengagement with Declan Donnellan's new ENO staging of the complete Rise and Fall of the City of Mahagonny, damned if I cared.

What really alienates is the smug, showbizzy complacency of the director's political posturing. We know we're in for it from the very start, when the back wall goes up and a solid line of stony-faced choristers marches silently forward to out-stare us across the footlights. It may be Jimmy Mahoney who ends up in court at last, condemned to death for not being able to pay his bar bills, but now we all know who's really on trial here. The adversarial style reaches its acme in Act 2, when tableau after tableau illustrating the excesses to which the men of Mahagonny have now descended - eating, loving, fighting, drinking - ends in the selfsame way: chorus to the front, house lights up, accusatory fingers prodding out into the auditorium. Just who do they think they are pointing at? Surely not us, the nice, liberal-minded, left-leaning, negative equity-beset nouveaux pauvres in the stalls?

Brecht and Weill, of course, wrote it for real, in a late-1920s Germany with fighting on the streets, Hitler waiting in the wings and exile beckoning from beyond the flies. Like Schnittke's Life with an Idiot, Mahagonny is a paroxysm of spleen against an unjust society. And like Idiot, from which the audience should emerge dripping with bodily fluids - but which ENO turned into a cosy April Fool's joke - Mahagonny needs to be staged as if the lunatics have taken over the asylum. It has to be played for real or it's nothing, and no amount of coy posing in suspender belts or soft-porn projections can convince that ENO's cast (least of all Lesley Garrett, who could well do with more support in her diaphragm and less in her bra) are anything other than opera singers slumming it. The real KO comes with the decision to amplify the voices, putting a screen between us and a text that should strike like spit in the faces of the front row. Bert Brecht meets the Blair Effekt.

One genuine theatrical frisson apart - as Sally Burgess's raddled Begbick momentarily turns her gun on the cruciform figure of Brian Matthews's God - this Mahagonny is as counterfeit as the dollar bills that shower down upon the audience during the final demo, each one stamped "sample", as if we really couldn't tell a fake when we saw one.

n In rep to 30 June at London Coliseum, WC2 (0171-632 8300)