It's all over when the fat bloke snores

THE SCENE is Klingsor's magic garden, about eight o'clock on a wet Wednesday night. Parsifal is listening to Kundry slowly seducing him, sinking into a great perfumed cushion of sound; a perfect moment of poisoned stillness.

The audience at English National Opera seems to be holding its breath. But what can that strange noise be, like heavy cotton being ripped in two? Can it be some unfamiliar percussion effect in the orchestra? Has the stage machinery gone into reverse, with a horrible grinding noise?

The singers are carrying on bravely, and here it comes again, sounding exactly as if someone is dying. The audience murmurs, and in a moment finds the perpetrator. It's some fat bloke, who has discovered the perfect spot to fall asleep and snore: the box right next to the stage. If he had been in the stalls, he wouldn't be half so audible; as it is, he is projecting directly into the auditorium, giving the performance of a lifetime. His companions are digging him in the ribs; the audience is muttering, outraged, and he is woken up and carried out, never to return.

Of all the occasions to choose, Parsifal is one of the least appropriate. Opera audiences are very hot indeed on the behaviour of their fellow members, and Wagnerians keener than most at ticking people off. Sometimes the second interval at Tristan erupts into a riot of mutual recrimination, as an idiot who has been conducting the love duet from the fourth row of the grand tier confronts his neighbour, rustling his way through a large bag of cellophane-wrapped sweets. And the code of conduct at Parsifal is even stricter than usual; by the best standards, one isn't supposed to applaud at the end of the first act, and if you start to clap at Bayreuth, you will be indignantly silenced by the keepers of the flame.

So there's something pleasing at this 30-second desecration. It's partly the pleasure of the appalling timing - there could hardly be a more conspicuous moment, or a more damaging one, to start snoring in any opera. And partly the feeling of "There but for the grace of God...".

The indignation at this awful behaviour is, in a way, more interesting than the awful behaviour itself. It's not so long ago that people went to the opera and talked all the way through it, as they do at the cinema these days. Indeed, so universal was the behaviour that operas were written in a style of noisy blandness, for the specific purpose of being talked over.

The English middle classes go to the cinema for an annual treat, so that they can keep up a running commentary of "Oh, Judi Dench, she lives opposite a cousin of mine - didn't you think she was awfully good in Mrs Brown?" Similarly, the sort of epic nonsense by Rossini which is now listened to with utter reverence was originally performed to a deafening ritornello by a chattering audience, and even if it had been possible in the din to go to sleep, your snoring would have passed as unnoticed as it would in the Odeon in Leicester Square.

If you actually tried to watch an English film, or sit in silence through a Rossini opera, I expect you would go mad; they are designed to be half- attended to while maintaining a constant stream of conversation. Only the smartest Italian opera houses maintain a strict decorum - in Rome or Naples, for example, the audience is always apt to start humming along, or even - something I once saw in Sicily - answering their mobile telephones in the second act of La Sonnambula. Of course, people never talked through Parsifal, but I wonder whether the respect due to the great monuments of Western art is not being unhelpfully extended to anything with any cultural pretension at all.

I couldn't help thinking that this artificial reverence for culture on the part of the audience has some connection with the apparently brutal loathing for it exhibited by some of the professionals; treating it as something which may only be wrapped in cotton wool, or smashed on the ground. The interesting thing about the other night is that it happened at an awful production of the opera, reversing every single one of the opera's meanings and redeemed only by the musical performance. The vicious desecration of Parsifal this production represents would not be interesting to a more relaxed audience, just as blasphemy is not shocking to anyone but the pious.

I'm not advocating that anyone starts cracking walnuts in the stalls when Covent Garden reopens, but you might like to consider whether the typical opera-goer's hissing outrage at breaches of propriety is not a strong encouragement for a producer who may be considering whether or not to set his production of Parsifal on one of the sidings at Clapham Junction.