When I agreed to be a slave girl in the Romanian National Opera's production of Aida at the Albert Hall, I had visions of being kitted out in a silken veils with a jewel in my belly-button. They abruptly vanish when, quivering half-naked under pitiless lighting, I am handed a pair of baggy brown knickers. A mixed lot of slave girls - tall, short, skinny, muscular, tubby - we represent something for every taste, but no one looks their best wearing Bessie Bunter drawers.

For a long time it looks as though this is all we'll get, until the wardrobe women bring in a pile of mud-coloured curtains and start draping and pinning. It's worryingly random. A tall, slender girl is swathed from neck to elegant ankle in exuberant folds, while a short endomorph makes do with a hessian tea-towel. I grab a clump of fabric and turn it about feverishly, trying to find anything resembling a head or armhole. Anne Demeulemeester couldn't have come up with anything as deconstructed as this.

With one trailing bit of fabric tucked into the sturdy knickers, and both arms kept close to my sides, I finally manage to work that curtain. The only safe place to leave my watch is inside my cleavage, which is already heading south since one bra-strap has had to be tucked under my armpit. Another slave is keeping her purse in her knickers, and she looks like she's giving birth every time she goes to buy a coffee.

This is the production's only night in London, and chaos reigns backstage. Characters are striding around in Asterix costumes, the tannoy announcements are in Romanian, and the assistant director speaks English in triplicate: "You, you, you - go, go, go - no, no, no!" The wardrobe mistresses lead the blond slave-girls off, one by one, to be fitted with itchy black tea- cosy wigs. Meanwhile all the men have been kitted out in hilarious long white skirts, platform sandals and tall headresses. With an imperious clapping of hands and a "kom wiz me!" the assistant director positions them at the top of the stairs and begins to hum a familiar march. "Pom, pom, pom, pappa pa-pom ... pappa pa-pom ... you go pom, OK. And ... go! GO! Stop! Why you no go?"

After curtain up, we are all relaxing and gossiping in the artists' bar - most of the extras are drama students - when we realise that a very strange noise is coming from the monitor which shows what's happening on stage. It's a hooting, honking cacophony which sounds more Mike Nyman than Guiseppe Verdi. A squad of black-clad figures have stormed the stage and begin to unroll a banner. There is a collective gasp as the words "Romania - Stop Jailing Queers" fill the screen.

A group of brawny Romanian stagehands push away their pints, spit out their Carpathia cigarettes and rush off. We follow them down to the stage and stand gazing at an equally stupefied full house. A chorus-line of protesters is being snapped by a skipping photographer. The soldier-extras are still standing to attention. "Smile, you'll be in the papers tomorrow," one of them is told. Backstage is pandemonium: one distinguished looking man is keening in distress; another, rougher and bearded, shoulders his way through, cursing volubly. The students seem to be torn between instinctive liberalism and a horrified sense that the show is sacrosanct, that politics should be left at the door. It's not difficult to feel sorry for the Romanians - they're luvvies, not law-makers - while admiring a dazzling "zap". As the protesters are dragged off, applause and cheers roll over us from the auditorium.

I and one of the slave-boys, who has put a rugby-shirt over his bare torso and brown knickers, run bare-legged round to the exit. He just has time to shout "Nice one, guys!" as they are hustled past. Security, in the form of the Albert Hall's redcoats, has arrived in force and there's a scuffle as the protesters are squeezed through the narrow lobby. One of them cries out, in a high, anxious voice: "There's no need for that!" and the doors swing to. Shaken, the Romanians have begun to sing again. Our own bit is over quickly. We grovel, slave-like, down the stairs and cringe piteously, waiting for our cue to rise and exit, but the director omitted to tell us about the 10 minutes of aria in between. Slaves are groaning softly and shifting their weight from one tortured limb to another - quite realistic, really. Then we rise, salute Nicholae Urdareanu, our splendid Ethiopian king, and hobble off.

In the interval, the mood is euphoric. The door-staff, expecting an evening of fat ladies singing, are joshing and grinning, and backstage the Romanian singers are roaring with laughter and slapping one another on the back. Even the doleful members of the orchestra, clutching their battered instruments and having a quick Carpathia in the corridor, look uncommonly cheerful.