Yet a source of much greater disturbance to me that night was the apparent refusal of both playwright and composer to pass judgement on the murky goings-on which they document so vividly. I also recall noticing early on a dubious tendency among my schoolmates and their supervisors to anticipate the next lurid event with palpable, almost physical excitement, as if they were watching a striptease or a bizarre circus show - which is, of course, exactly how the Animal Tamer introduces the whole opera at the start. The extent to which you can or cannot cope with those sorts of feelings, not so far from outright voyeurism, may well determine the extent to which Lulu is your kind of opera.
Whereas Wozzeck, Berg's first opera, has received fairly steady approbation from the public and from Berg's fellow composers alike, Lulu divided opinions right from the start. It's not hard to see why. Wozzeck documents the plight of a penniless soldier driven by jealousy to murder his girlfriend. This is the standard stuff of opera - a kind of latter-day Carmen. Lulu, on the other hand, is an adaptation of two sordid plays by the turn-of- the-century Viennese writer Frank Wedekind, with no moral at all. The heroine is surrounded by over-sexed, obsessive males who make her life hell. Lulu courts their attention, but shows little genuine affection to anyone. She brings death to her admirers, but ends up being murdered herself at the hands of Jack the Ripper. The plot has no evident point and Berg is careful to avoid giving it one: the music is sensuous, supremely crafted, yet emotionally cold and frequently remote.
None of Berg's contemporaries knew what to make of all this. When he unexpectedly died in December 1935, Berg left the orchestration of the last act incomplete and his widow Helene asked Arnold Schoenberg, Berg's mentor, to complete it. Schoenberg accepted in principle, then refused on discovering an anti-Semitic remark seemingly added by Berg to the libretto of the final act, possibly to court favour with the Nazis. Berg's close friend Anton Webern also shied away from the task, as did Schoenberg's teacher Alexander von Zemlinsky. The refusal of these two is indeed puzzling: the job would have been straightforward for anyone as familiar with Berg's idiom as Webern and Zemlinsky were, both having conducted several Berg premieres.
In any case, events overtook them: the opera was premiered as a two-act torso in Zurich in 1937, and continued to be thus heard for over 40 years. Discouraged by the negative responses of Berg's fellow composers, Helene took against the entire project and forbade the opera's completion. She even cited messages transmitted by her husband from beyond the grave supporting the embargo. The orchestration was finally completed from Berg's strikingly clear sketches in the 1970s by the composer Friedrich Cerha, who worked on the job over a period of 13 years with the connivance of Berg's publishers, but entirely unknown to the composer's widow.
By the time Pierre Boulez unveiled the whole work at the Paris Opera in 1979, three years after Helene Berg's death, the musicological industry had caught up with Berg following the revelation that, for the last 10 years of his life, he had carried on a secret (albeit unconsummated) liaison with a woman in Prague. It was discovered that Berg's 1926 string quartet Lyric Suite was saturated with references to this liaison - musical spellings of his and his beloved's names, elaborate musical descriptions of their meetings, portrayals of her children and so forth. Similar autobiographical codes had been discovered in the slow movement of the Chamber Concerto and in the Violin Concerto, so that when Lulu finally appeared Berg scholars positively rampaged over the completed score, discovering a hidden reference here and a secret numerical code there. It was all quite entertaining, of course, and doubtless earned an innocent doctorate or 10. Yet I wonder if I am alone in feeling that much of this activity merely succeeded in diverting attention away from the music itself. To borrow the late Hans Keller's brilliant phrase, people were thinking about the music instead of thinking music.
And no wonder they were, for attending a performance of Lulu can be a very discomfiting experience. Initially the musical style seems more ingratiating than Wozzeck: the expressionist outbursts are far fewer than in the earlier work, the harmonic language is lush and flirts with tonality, with a rich and often jazz-tinged orchestral palette that highlights shimmers from the vibraphone and an alto saxophone's doleful wailing. The work also abounds in blatant displays of compositional expertise: mirror forms, complex 12-note permutations, fughettas, canzonettas, inventions and chorales, all carefully annotated as such in the score. Yet, after a while, you may well wonder what all this scrupulously crafted elegance is doing as an accompaniment to the awful happenings on stage.
The great French composer Olivier Messiaen, an admirer of Wozzeck, seems to have found the discrepancy between action and music in Lulu positively annoying: "The subject of Lulu is repugnant and should have been treated as an example of madness," he asserted, "but its realisation in the music is academic and, as a result, a failure... All one finally hears is a grey serial score." The severity of Messiaen's judgement can probably be explained both by his distaste for the plot and by his repeatedly professed loathing for jazz, so prevalent throughout Lulu. Berg scholars have nevertheless noted the seeming coolness of the music in the face of the seediness on stage enough to wish to justify it.
The standard explanation runs that, by maintaining a certain distance from the encroaching debasement, the composer is able to evoke our compassion for Lulu's plight the more poignantly. This view has never convinced me, partly because it assumes that Lulu is a figure for whom we should feel compassion at all. Recent commentators have indeed seen Lulu as an innocent victim of her surroundings, of the fantasies her numerous male admirers project on to her. But the reality of this opera is surely more ambivalent: Lulu shows every sign of enjoying the attention and the fantasies, despite the trouble they cause. In Act 2, her latest husband, Dr Schon, is driven to distraction by discovering a whole series of clandestine admirers hidden throughout his own living-room. Lulu, on the other hand, encourages them, and the music Berg provides does not suggest any qualms that might lead her to shoot herself, as Dr Schon subsequently requests (she shoots him instead). What, for that matter, is one to make of someone who reacts to her first husband's fatal heart-attack by stroking him and singing, in one of the most alarmingly beautiful moments of the entire score, "He'll jump up in a minute, he's just acting"?
The Viennese critic Karl Kraus, whom Berg revered, even suggested that in the final scene of the play Lulu is actually pleased to encounter Jack the Ripper, that she somehow wants him to kill her. In fact, the music accompanying their grim encounter is indeed a reprise of love music from earlier in the work; and, as if to emphasise the unnerving parallel, Berg requests that Dr Schon and Jack be played by the same singer.
No, any attempt to tame this opera, to reduce it to a nice, neat moral tale - according to whatever code - is doomed. In an age dominated by political correctness, Lulu remains distressingly incorrect and admirably elusive. It is one of the few operas with characters as complex and perverse as real people and, as such, for me at least, the key opera of the 20th century.
n 'Lulu': at Glyndebourne from Monday (booking: 01273 813813); broadcast live on C4 on 27 July; at the Proms/BBC Radio 3 on 23 Aug (booking: 0171- 589 8212)