The young audience, ranging from pre-school age to a more sensible ten or 11, is fidgety: parents lean across their charges with a restraining hand, or an instructive word in the ear, and there is the occasional shriek. My four-year-old son - admittedly on the young side for this branch of musical education - clambered on the seats and demanded peanut-butter sandwiches Q one of which was inadvertently dropped over the parapet onto heads below.
But between the disturbances, the children do listen: to the arresting depiction of a train in Arthur Honegger's Pacific 231, to a display of trombone virtuosity in Gordon Jacob's concerto, to the increasing insistence of the side-drum in Ravel's Bolero. My son enjoyed the loud bits in Finlandia, when I whispered to him about dark forests and galloping horses, even though he did ask to go home when we got to the quiet bit.
Surprising as it may seem, this is an audience close to Harrison Birtwistle's heart. Despite a popular (and ill-founded) reputation for producing appallingly loud, discordant music, and for having a dour, introverted, bear-like personality to match. Birtwistle cares very much about reaching people, about making music accessible. The family concerts were his idea when he began a five-year contract with the LPO as composer-in-residence two years ago.
"I think children are much more receptive to music than we are," he says. "They have fewer prejudices, and there are more things you can play them."
I met him towards the end of a retrospective of his work. He emerged from a rehearsal of Panic, tired and bleary, like a person with musical jet lag Q but not in the least gruff. So much of his work has been played in a short space of time that he says he has the bewildering sense of never quite knowing what is coming next. "I'll be glad when it all goes away. But music is performance, and I like the rehearsals. I prefer them to the concerts, because I feel I'm still in control, to some extent."
In terms of what Birtwistle calls the prejudices of adult listeners, Panic has called forth a great many. A dynamic, dramatic, and, yes, loud piece, in celebration of the god Pan, featuring solo saxophone and drum-kit, Panic was premiered at last year's Last Night of the Proms - to howls of protest. Birtwistle's music was pilloried, one newspaper reader alleging that the players in Panic must have been making it up as they went along, as such noise could not possibly have been composed.
"I'm only here for a dare, for a bit of punishment," joked an LPO violinist at the start of the rehearsal, not involved in Panic but listening out of choice. "Hope you've got your ear plugs in," added a percussionist. But at the end, the reaction was more reflective. "I'd been led to expect this great blast of anti-culture," said a tuba player, "but, actually, it's rather a good piece. "
Birtwistle claims not to care what his audience thinks of him. What he does care about, manifestly, is whether enough music, of different kinds, is reaching enough people. "In London we have three or four orchestras all vying for the same audience. There is a lot of music out there, but because most concerts are aimed at a middle-of-the-road, music-loving audience, only about 25 per cent of the classical repertoire gets played. There are a great many pieces in the popular repertoire, too, that are not played at all."
Programming concerts for children has enabled him to break with many of the constraints and expectations of more conventional programmes. "There are certain considerations, like their concentration span, and the fact that children don't really like quiet music - because in quiet music they can hear themselves talk. We stick to single movements, and would never play a whole symphony. But you can be more eclectic, and you can juxtapose different things - because kids don't care if you have The Ride of the Valkyries followed by something French. I quite like all that. The concerts are not meant to be coherent - they're meant to keep the ball in the air, and keep the interest going."
Quite often a programme will be devised to feature a particular instrument Q last month it was Warwick Tyrrell on the trombone, who also played the didgeridoo - and Birtwistle believes this is good for the players, too. "They don't normally get the chance to play solos, so they enjoy that."
He hasn't yet included one of his own works in a family concert; although he is debating whether his piece for tuba and orchestra, The Cry of Anubis, might be suitable for slightly older children.
But one of his operas, Yan Tan Tethera, a "mechanical pastoral" about sheep and shepherds has already proved a big hit with schoolchildren, in one of the orchestra's education projects. The London Philharmonic has a growing commitment to working in schools, sending its players to collaborate with teachers, helping the children to listen, compose and perform. Birtwistle has taken a keen interest, although he confesses that he only visits schools occasionally: "I'm not terribly good at it, and there are other people who are better. I like children - but I don't know how to deal with them particularly well."
In the Yan, Tan, Tethera project, children explored the subject matter, devised something of their own, and then came to a performance of the opera. "They were from a very difficult area, with a big ethnic mix, and most of them had never seen a live instrument before," says Birtwistle. "When they came to the performance, the teachers said they had to be put near the door, in case they needed to get out. But afterwards I felt like the Pied Piper. They all came round me and were saying things like, 'Man, where do you get those noises from?' It was really touching because they had no problem with the music at all. Whereas lots of adults would have been saying, 'What was that all about?'."
Harrison Birtwistle was born in Accrington, in Lancashire, in 1934. One of his first forays into composition was a piece he wrote aged about 12 for clarinet and orchestra, called The Piper at the Gates of Dawn, based on an episode in Kenneth Grahame's The Wind in the Willows; this idea provided the starting point for Panic, although Grahame was soon jettisoned for something more wild and exuberant.
Birtwistle studied clarinet at the Royal Manchester College of Music, where his contemporaries included Peter Maxwell Davies, John Ogdon and Alexander Goehr. But it was not until 1965 that he devoted himself entirely to composition, selling his clarinets and travelling to Princeton on a Harkness Fellowship, where he completed his first opera, Punch and Judy.
Up until this time, Birtwistle earned his living teaching music at Cranborne Chase, an independent girls' school in Wiltshire. "I enjoyed it a lot. There were no discipline problems, and the school had a big accent on music. Many of the girls played instruments, and I wrote music for them, and introduced them to a lot of music they didn't know, particularly early music."
Although not particularly au fait with the music requirements of the national curriculum, Birtwistle maintains that there is not enough real creativity going on in schools, and he is angry at the way the arts are forever getting squeezed. "I've seen kids on television programmes doing things with synthesisers and it seemed to me to be pretty boring. Too often they seem to be doing things that they already know. But a child is a creative animal: right from the beginning, if you give them a piece of paper, they'll draw on it, or do something with it . . . Vandalism, I think, is a creative act, an act of negative creativity."
At his own school, there was no music to speak of, and his parents, who did not play an instrument themselves, arranged clarinet lessons for him outside. But there was, at least, singing. Birtwistle deplores the fact that today's children are singing less and less, some of them not at all.
"It's the one thing we are all given, a voice. We sang hymns in assembly every morning and we sang 'community songs': songs from the 18th century, folksongs, canons, songs in parts. It's a very simple thing - but it's not happening. "
Another thing that makes him angry is that people are being programmed not to listen to music properly. "If you trawl the airwaves, they're full of garbage, aren't they? Music has become something that is there to be on, but not to be listened to. It's there to get you through the day, while you're doing the washing-up, or whatever. But there is a problem with music which is that you have to sit down and listen to it."
Even Classic FM, he fears, is contributing to this dilution of listening power, and he only reluctantly accepts the argument that to broaden the audience for classical music is better than nothing. "There's another audience out there that is not really catered for," he says. "An intelligent audience, which doesn't necessarily want to come to something as severe, if you like, as contemporary music, but could accept a more eclectic approach to it."
He cites two projects he has masterminded in the past 18 months, both of which filled the Queen Elizabeth Hall: the first, a weekend devoted to brass instruments, involving not only adventurous concerts (The Cry of Anubis was written specially), but also seminars, masterclasses and sessions for schoolchildren; the second a weekend on percussion. A third, on singing, is in the pipeline.
This approach works, he argues, because by the time people listens to the concert, "the music has already become part of their world". It enriches orchestral life, too - crucial, he says, if the orchestra is not to end up as some sort of dinosaur, playing nothing but the classics. "I don't understand what the problem is with music: for me, it's something very exciting and wonderful, but people are more prejudiced about music than anything else. I don't want to preach, because my job is to write music. But I know there's a lot of different music out there. People go on about music being elitist, but to me, it's an exclusive club with an open membership; music belongs to anyone who wants to hear it."
Next season's family concerts are on November 10 and December 1 1996, and February 9 and May 4 1997.
Children's concerts, also at the Royal Festival Hall, are on December 4 1996 and March 12 and May2 1997, tel: 0171 546 1666.
* Secret Theatres, music and dance inspired by the music of Harrison Birtwistle devised by 200 children from the London borough of Merton in collaboration with the London Sinfonietta and Richard Alston Dance Company, is at Wimbledon Theatre, July 12, 7pm.