It is not often that the creators of a new opera, before its premi re, come to a university music department and answer questions about it. But that was what happened last month when Sir Harrison Birtwistle and Russell Hoban, respectively composer and librettist of the new Glyndebourne commission, The Second Mrs Kong, addressed an Opera Colloquium at King's College, London.

The occasion was one of the first visible signs that Birtwistle, one of Britain's most highly acclaimed living composers, had taken up the new Henry Purcell chair of composition at King's. The next public event is an invitation-only Principal's Concert on November 21, to inaugurate the chair, at which music by Birtwistle and Purcell will be performed.

Certainly, it seemed that a large proportion of the King's music department's 75 undergraduates and 40 postgraduates was crammed into Room 6C to hear Birtwistle and Hoban talk about the opera that early reviews have described as "a triumph" and "a witty, often wildly surreal invention". It was a discussion that ranged from the fairly technical -- why did Birtwistle write a prominent part for accordion in his score? Did Hoban rewrite his libretto after the composer started work on it? -- to the almost inevitable question about whether Birtwistle's music was accessible to the man in the street. "Who is the man on the street? I've got a problem with the man on the street," he answered, to laughter. Birtwistle is used to being told that his music is inaccessible, but more and more people seem to be getting round to liking his idiom. Witness the success of his 1986 Earth Dances, which has now been programmed by some ten orchestras worldwide, and was performed at this year's Proms by the Cleveland Orchestra.

Birtwistle can be a man of few words. He seems only too conscious how inadequate words can be in describing much musical experience. His head of department, Curtis Price, is at hand to amplify matters; to explain, for example, that this is a 60 per cent appointment for Birtwistle -- allowing him time for other occupations such as his work as composer-in-residence for the London Philharmonic Orchestra, across the Thames on the South Bank.

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"Harry will be teaching postgraduate students mainly, and a few selected third-year undergraduates," says Professor Price, "also giving general lectures." To which Birtwistle adds: "I'd like to think I could embrace all the people who are doing creative music." As a question at the colloquium showed, his presence at King's has enabled a number of students there to attend rehearsals for The Second Mrs Kong. Indeed, one third-year composition student spent most of the three weeks before the opera's premiere as Birtwistle's amanuensis at rehearsals.

As for his students in general, Birtwistle says that he hopes he can teach them "how you can discover yourself" -- and pass on to them "simple technical things . . . and observations from experience. Very often students can't see the wood for the trees of their own ideas."

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By all accounts, it was not easy for the young Birtwistle, a working-class lad from Accrington, when he won a clarinet scholarship to the Royal Northern College of Music in the 1950s. He describes himself as "a composer only in my head" in those days. Instead, other people, such as his contemporary John Ogdon, later better known as a piano virtuoso, wrote music for Birtwistle the clarinettist to play.

Music historians now talk of him as a member of the "Manchester School" that arose in the 1950s and 1960s to challenge a somewhat conservative British musical establishment. But Birtwistle says he felt like a "beanbrain" among others such as Ogdon, Peter Maxwell Davies, Alexander Goehr and Elgar Howarth. But he did get from his fellow students in Manchester "a sort of spirit," he recalls. "We were quite pretentious. We were taking it all on -- taking Beethoven on, as it were. it was quite romantic, really."

He has not played the clarinet for more than 20 years -- no, more than that. "It's quite a responsibility playing an instrument, " he says.

So it is as a teacher and composer that Birtwistle, 60 this year, has made his living. He was music director of the National Theatre for a spell in the 1970s, writing music that he says will never be published. "My theatre music was written for a production, for an occasion. As far as I am concerned, when that occasion's finished, then the pieces have." What have survived are the operas and other vocal and instrumental works from short pieces for brass band to the ambitious Gawain, recently revived at Covent Garden. (The Second Mrs Kong took a "very fast" 18 months to write).

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Most of Birtwistle's teaching has been in the United States. He went to Princeton on a Harkness fellowship, and has taught at Swarthmore College and the universities of Buffalo and Colorado. At Buffalo he invented a course called Rhythmic Analysis -- how time works in music, and what rhythm means.

At King's, Curtis Price says the details of "how we can best employ Harry" are still to be worked out: but certainly Birtwistle will be working with as many composition students as possible.

"I was talking today about what an idea is -- I mean, what you actually start with. Why you would write a piece for piano, cello and clarinet, which one boy was thinking of. I asked him, 'Are there certain things implicit in the instrumentation that define what the music's going to be?' Actually I would hate to write a piece for piano, cello and clarinet -- it's not in the nature of the music I write . . . That's my way of thinking, but I would never pass that on to (students). You can't do that."

Does he think his work gets imitated? Birtwistle chuckles. "All the worst bits... I've got a lot to answer for! Not so much now, but in the 1980s there were a lot of composers writing music like mine." (He refuses to name any, however.) Looking back on his own work, too, he often sees things that could be improved: "I always feel that everything I do is a sort of approximation of what is possible. I think that's common to a lot of people: every new beginning is another chance."

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