Exactly a year ago Sir Simon Rattle sat in Chris Smith’s office and gave the incoming Secretary of State for Culture a friendly warning. “I told him he was going to be hearing a lot from me and he might find some of it uncomfortable,” the conductor recalls. It was, perhaps, new Labour’s first intimation that it would not be getting an easy ride from the arts world.

Simon Rattle surprised Chris Smith on that May morning with his agenda. “He thought I would want to discuss orchestras and concert halls and theatres. I told him my main concern was music in schools,” he says.

Since then Sir Simon has become a man on a mission, stung into action, first by alarming reports of the decline of instrument tuition and then galvanised into fury by the downgrading of music in the primary curriculum. He sees this as a threat to the musical fabric of the nation and speaks of “the betrayal of an entire generation” and “the death of the imagination”.

While the Government has been able to dismiss the critics of “cool Britannia” as whingeing pop stars, it has had to take Sir Simon’s warnings far more seriously. Six years ago he led the fight to get music established in the national curriculum and Whitehall has since been desperate to keep him “on side”. Education Secretary David Blunkett has appointed him to the Department for Education and Employment’s National Advisory Committee on Creative and Cultural Education, which is due to report in September, and Mr Smith has invited him to help draw up plans to use lottery funding to support music teaching and instrumental tuition.

No one should imagine that this will stop Sir Simon speaking his mind. “I have no choice but to speak out,” he says. “It’s payment for the knighthood - if you have any kind of leverage in a desperate situation, you must use it. I wasn’t expecting to have to be an evangelist for the arts in education but it seems to have happened, and I’m going to carry on exploiting whatever irritant value I may have.”

He warmly endorses The TES’s Music For The Millennium campaign, which he says “should have the support of every thinking musician in the country”. He also feels vindicated by the results of the survey The TES commissioned to launch the campaign. While officials briefed that Sir Simon’s claims were “alarmist” and Mr Blunkett publicly insisted the Government remained “absolutely committed” to music in the curriculum, the survey found that as a direct result of the proposed changes, one in five primary schools was planning a reduction in music teaching and some schools were dropping the subject altogether.

“Whatever the politicians say, Chief Inspector of Schools Chris Woodhead is telling schools they will not be assessed or inspected on the national curriculum programmes of study in music, so of course it will get cut,” says Sir Simon. “Most teachers are overworked and underpaid and have been told they are crap for years, so it is hardly surprising if they welcome any reduction in their workload.

“Yet what right have we got to consider ourselves civilised if music isn’t a central part of what we are taught?” That Sir Simon still has time to campaign so passionately on behalf of the grass roots speaks volumes for a man who has not only run the City of Birmingham Symphony Orchestra for the past 18 years but is also in huge demand as a guest con-ductor with the world’s great musical ensembles, from the Vienna Philharmonic to the Boston Symphony. But music education has always been at the core of his work, and under his leadership the CBSO has developed a schools programme that is the envy of every other local authority.

Typically, he insists the credit lies not with him but with his players. “The impetus came from the musicians. They know the word needs to be spread and they are passionate about it. Education has become one of the lynchpins of the orchestra, and at any given time there are about 35 musicians going around the schools, often in under-privileged areas.

“The inspiration is two-way - they go into a classroom with just their personality and their instrument and they return to the orchestra a different person.”

For many in Birmingham, Sir Simon’s baton has seemed more like a magic wand. When he finally leaves the CBSO this September, his will be an almost impossible act to follow. He has transformed the provincial orchestra he took over at the age of 25 into a world-class ensemble, and in the process helped to generate a new civic pride.

He persuaded one of Britain’s crustiest old aldermanic authorities to build the finest symphony hall in the land and ensured that London could no longer automatically regard itself as the unrivalled capital of British music. He helped put not only the CBSO on the map but the entire city, and to find someone who can “do a Rattle” has become the ambition of every arts administrator in Britain.

Above all, Sir Simon, now 43, has never forgotten his own roots as a “middle-class Scouser” and musical product of the state school system. His businessman father, Denis, was an amateur jazz musician and his mother, Pauline, worked in a record shop. Sir Simon decided he wanted to conduct after he heard a performance of Mahler’s second symphony in Liverpool when he was 11. His sister, Susan, worked in a Liverpool library and would bring him home dozens of scores.

“He was a normal boy,” his father once insisted, although the picture he painted of his son was anything but usual. “He would sit up in bed with these enormous orchestral scores in front of him, turning over, reading like other kids read a comic.” Then with mock regret: “He went all square on me. I thought I was going to have a wonderful jazz drummer to accompany me in my old age. Now look at him.”

At 15 Simon Rattle was conducting the Liverpool Youth Orchestra, and at 19 he won the John Player conducting competition in Bournemouth. At 21 he became the youngest ever conductor at the Proms and made his Glyndebourne debut the following year. Somewhere he still managed to fit in a degree at Oxford - surprisingly not in music, but in English. There was a brief spell as assistant conductor at the Scottish Symphony Orchestra before he went to work his miracles in Birmingham.

He has an easy and attractive manner, but there is an intensity about him that belies the casual glamour of his almost rock star looks. When he puts down the baton at Birmingham to freelance with orchestras around the world, he says, he will be “even freer” to pursue his crusade on behalf of music in schools.

Since he started his campaign earlier this year, his weekly postbag has rivalled War and Peace in length and intensity. “I get so many letters from people who have felt abandoned, it makes me want to weep. Frankly, we still haven’t made enough noise.”

His greatest fear is that music in British schools will go the same way as in the United States, where his two sons, Sasha, 14, and Eliot, 8, live in San Francisco with his first wife, soprano Elise Ross. He describes with excitement the joy of watching them learn to read music or “crack the code” as he puts it, but says music is totally “unimportant and marginalised” in American schools.

“Britain could go that way. School music education has been one of our glories, and for 40 years our youth orchestras have been the lifeblood of music-making and the envy of the world. Over the past five years we have seen all these achievements damaged.”

Sir Simon recently told the arts editor of The Times that Britain was facing the possible “death of music”. Ask him if he was overstating the case and he replies that if anything he understated the danger: “What we are facing is the death of the imagination.”

He goes on to tell a story of a school in California where his ex-wife was working with teenage girls from the ghetto. “The most chilling thing was that she started talking to them about using their imagination and only two out of 10 knew what she was talking about.”

Of course, he has a vested interest in musical education - for if the pool of young players dries up, the big professional orchestras will eventually be affected. But his concern lies deeper than that, and he has obviously thought long and hard about the overall importance of music in education.

“Music can have an extraordinary effect on every area of learning. It shifts the emphasis from observing to doing. Children have to work together to create a performance, so that every type of social, organisational and co-operative skill is used and everyone can contribute,” he says. “Music is not merely good for the soul, it can promote literacy and numeracy across the board. Everybody needs music in their life as a way of decoding a hostile universe. Education has become too narrow, and specialisation too early has been very damaging.”

Sir Simon has no political bias, and he balances his criticisms of the present government with a tale about a meeting with the late Sir Keith Joseph, Tory education minister in the mid-1980s. Sir Keith was expressing concern about Britain producing too fewworld-class soloists and asked which music college the Government should fund. Sir Simon told him to concentrate on primary schools.

“Even very intelligent politicians don’t seem to grasp the long-term effects. He was incapable of seeing that you must start with very young children if you are going to produce great musicians. That holds good right across the spectrum, from pop to classical.

“Music is for everybody, and, like many of the other marvels of humanity, needs to be inculcated as early as possible.”

He fears the effect of cuts may be irreversible because there is little chance children over 11 will ever start to learn an instrument. “The sharpest drop in the number of children learning instruments is among five to 11-year-olds, the generation first hit by the cuts. Predictably, the decline is also almost entirely among children whose families would never be able to afford music lessons. Yet most of the best musicians I know come from working-class backgrounds. We risk losing all that talent.”

Sir Simon will do his damnedest to ensure it is not lost. Music education may never have been under greater threat. But it can never have had a more eloquent champion.

Sir Simon Rattle’s farewell concert with the CBSO is at the Birmingham Symphony Hall on August 31