“Try to make it as liquid as possible,” instructs Cecilia McDowall. At the piano Richard Charlton, 15, picks up the pulse of the music again and this time gives the part a pleasingly rippling effect. McDowall nods in approval, but then violinist Tarik Amer, 16, wants to know how best to phrase a certain bar. And there’s no one better qualified to tell him, for McDowall is not a school music teacher but the composer of A Draught of Fishes, the work they are rehearsing.

Not all young musicians are as fortunate as the boys of St Paul’s school in Barnes, London, in having a living composer on tap to offer advice on how his or her work should be played. But, thanks to the Schubert Ensemble, increasing numbers of young players in schools all over the UK are cutting their musical teeth on a repertoire of chamber pieces especially written by leading names in British music.

The five-member ensemble spends as much time as its busy schedule permits in schools, running workshops for young musicians, including residencies at three schools in the West Country. Three years ago, it launched Chamber Music 2000, an ambitious project to build up a substantial collection of new works for piano and small string groups suitable for young people.

CM2K was set up with pound;90,000 in sponsorship from a variety of trusts and individuals, but it had other assets: an influential patron (the conductor Sir Colin Davis) and an enormous amount of goodwill from the musical establishment. Some 60 pieces have been commissioned, about two-thirds of which have already been published. Participating composers include Judith Weir, Sally Beamish, Stephen Warbeck, David Matthews, Alwynne Pritchard and Roxanna Panufnik. All have contributed for nominal fees.

“There’s a lot of enthusiasm from the composers and the young musicians,” says Simon Blendis, the Schubert Ensemble’s violinist. “We were always being asked what modern5 chamber music there was to play in schools. We realised there wasn’t really anything in the repertoire.”

Between them, Blendis and the Ensemble’s pianist, William Howard, decided to do something about it. “We believe in chamber music,” says Blendis. “It’s a tremendous learning ground for young musicians because it teaches you about playing together and it instils a terrific confidence. It’s brilliant ear training and it improves intonation and rhythm. Its benefits are immeasurable.”

Composers were asked to write easy pieces that preserved the integrity of their own musical language. The 40 works so far written have been published by BMIC, and the Schubert Ensemble has recorded a CD of 20 of the short pieces, The White Room, released by NMC Recordings.

The progressive music department at St Paul’s quicly saw the advantages of the project. “We wanted to develop chamber music and contemporary music,” says Mark Tatlow, director of music at the school. “The Schubert Ensemble’s initiative seemed unique.”

The CM2K works fill a major gap, he says. “There is now such an emphasis on composition in the modern exam syllabus, and pupils know all about pop and rock and they know about the classical heritage. That means in the exam compositions we get a lot of pop and a lot of pastiche. What we don’t get is contemporary classical composition.” The school is integrating several CM2K works into the exam curriculum.

Back in the main hall, a trio of St Paul’s boys is struggling with a piece by Michael Finnissy called Bright Future Ignoring Dark Past. They are more than adequately equipped technically but are uncertain about the work’s meaning. “What is this?” asks 16-year-old pianist Danny Segall. “Where are these shapes and phrases going?” William Howard, who has been coaching them through the work, pauses. “It’s a very cerebral piece,” he admits. “I’m not asking you to like it. But let’s allow the piece to unfold and suspend judgment until we’ve performed it. You might not be able to identify with it, but playing it is going to give you valuable experience.”

The boys still aren’t satisfied. “We need to know what it means,” says cellist Tom Stern, 16. But violinist Edward Saklatvala, also 16, is more relenting. “I suppose we can just lay it out as the piece is written and let the audience reach their own conclusion.”

There follows a discussion about the composer’s intention in which the young musicians challenge Howard as intellectual equals - which makes him purr with satisfaction, for Chamber Music 2000 was set up precisely to stimulate young minds in such fashion. At the end of the afternoon the trio play the work with thrilling confidence.

Cecilia McDowall is also delighted with the way the boys perform her work. “As a former parent at the school and a composer I was aware that there simply weren’t these works in the repertoire,” she says.

“Many young people have never had the opportunity to play chamber music. Now they can hear a whole spectrum of contemporary music. We were asked to write works within their capabilities but in none of the compositions does the composer compromise on style. It’s serious music for serious young players.”

Further information: www.chambermusic2000.comFor information on the Schubert Ensemble’s educational projects, contact Ann Senior at senior.mgt@dial.pipex.comFor scores contact BMIC on 020 7499 8567.The White Room CD is available from NMC Recordings on 020 7403 9445, pound;12.99.The Schubert Ensemble will give a concert at St Paul’s school tomorrow with pupils of the school; the programme will include a new work by Cecilia McDowall. Tickets: 020 8748 4048