On the door of the church in Totnes, Devon, a notice announces that “major-ette training” has been temporarily suspended and the organist is unwell. Inside, a stern young woman sits in the regular organist’s chair, playing Bach as though her life depended on it. Which is not far from the truth. Her name is Olga Yefremova, she comes from Odessa, in southern Ukraine, and this is the first chance she’s had in months to practise her profession. Odessa’s only pipe-organ no longer works, because the city’s electricity supply is too weak to drive it.

But why has Olga travelled all the way to this remote corner of Devon to play her music? If I can wait a little, she explains in halting English, all will be revealed. We drive along a twisting lane through a valley until we find ourselves in a grassy courtyard - and in the Middle Ages. A stone manor house, a huge raftered hall, and gardens sloping away into the bosky distance: this is Dartington Hall, where Olga is a student at the annual summer school.

When a pair of rich visionaries called Dorothy and Leonard Elmhirst bought Dartington in the Twenties it was a ruin. They turned it into a place of cultural experiment, to which artists from all over Europe were immediately attracted. Many were musicians fleeing Nazi Germany, and more than a few made it their second home.

It also became home to an educational idea by the German pianist Artur Schnabel, who wanted to found a school where musical excellence could be passed down the generations. The director of the Edinburgh Festival was not interested, so Schnabel set up his school in Bryanston in Dorset, where it stayed for five years before moving to Dartington. This year’s summer school, which starts tomorrow, will be Dartington’s 50th.

From Jews in the Thirties to modern-day Ukrainians such as Olga - and the Serbs and Croats who mingle here in musical comradeship - refugees have long been beating a path to Dartington’s door. Two years ago a group of Polish students arrived unannounced after busking their way across Europe. They couldn’t pay for bed, board or tuition, but when they pitched their tents in the grounds, the school’s administrators admitted defeat, and invited them in to classes.

As an amateur pianist and one-time chorister, I was curious to see what the Dartington process feels like. For it maintains a unique balance between professional and amateur: it’s not a holiday-camp with music thrown in, but neither is it a forcing house for cloistered high-fliers. The man sitting next to you in the piano masterclass may be a retired surgeon, or he may be the next Simon Rattle.

Talking of whom . . . this is where the 13-year-old Rattle came as a student, chaperoned by his parents, and where he took his first steps to becoming a conductor. It is also where Nicholas Kenyon, controller of Radio 3, used to hump pianos around as a star-struck teenager, and where Stravinsky presided for a summer in the Fifties. Everybody who is anybody in British music has either studied here or taught here, or both. One would be pressed to name a single prominent British conductor who has not passed through the choir into which everyone at Dartington is conscripted, divas alongside growlers, and which gathers for practice at dawn.

We will draw a veil over my performance in Joanna MacGregor’s piano masterclass. Suffice to say the infinitely superior pianists waiting their turn were very understanding. They were also full of surprises. I’d stereotyped the burly gent who whirled through Schumann’s daunting Kreisleriana as an up-and-coming professional, but he turned out to be a former airline pilot. The nervy youth who followed him - with some magisterially rendered Debussy - was a professor’s son on annual leave from the Israeli army. A Japanese girl played Ravel brilliantly, but without regard for the composer’s expressive instructions in the score; it emerged that neither she nor her Japanese teacher could understand French.

The studious blonde who played Liszt with such authority was Alison Farr, a 16-year-old from Bournemouth who was recently voted Audio Musician of the Year. During breaks between classes she passed the time juggling, five balls at a time. That’s talent for you. Her mother says she first played the piano as a one-year-old - which reminds me of a photo of Rattle, showing the infant maestro at the keyboard at a similar age. Perhaps I have met the new Simon Rattle.

Each evening there are concerts, some performed by tutors and some by students. One night we heard a recital by a young cellist from the Russian city of Kazan, and were struck by two things: her glorious playing, and the fact that her instrument is not much better than a cricket bat. When it emerged that she and her family live in extreme poverty, the entire school - old and young, amateurs and pros - dug into their pockets to help buy her something decent to play on.

Thirty teenagers had travelled the rather shorter distance from east London. They were members of the Hackney Youth Orchestra, making its annual visit. This is an inspirational story in itself, as their conductor, Nick Ridout, explained.

Ridout studied horn and piano as an undergraduate at Dartington College of Arts, a full-time college run by the same trust that operates the summer school. He had been a teacher at Woodberry Down junior school, in Hackney, where he set up a small orchestra. The orchestra had gone from strength to strength - performing at the South Bank in its second year - but he was both disappointed and puzzled at the way his players abandoned their music when they went on to secondary school.

“Then it dawned on me,” Ridout says. “Not one of the local secondaries offered any string tuition.” So he set up another orchestra, for teenagers from all over Hackney, which was also successful. The musicians went on holiday courses, including a week’s intensive training at Dartington. That was in 1992; this year they will be back as usual,including some players from the original orchestra of 1990.

“Socially and musically it’s enormously valuable,” says Ridout. “Lessons where they play for an hour a week and then put the instrument away until the next are a virtual dead end. This is the opposite, and it also teachers them the importance of collaboration. A lot of my players forge lifelong friendships here.” There are more girls than boys; all pay Pounds 130 for their week, and most bust a gut to come back. Ridout has lost count of the number of young people whose lives have been changed by this experience. Some who began with no training have gone on to become professional musicians, others have been reclaimed from no-hope drug dependency.

Indeed, as the days pass, the place itself starts to work like a drug. One savours the variety of sounds which hover in the air as one walks past the practice rooms - Beethoven from one window, Chopin from the next, Schubert from the one after that. One joins the loafers round the open-air pool - “all asses will be shown” reads the waggishly-altered notice at the entrance, in accurate reflection of the unbuttoned spirit of the place.

Strolling in the grounds at six in the morning, I found a group of fledging flamenco guitarists trying out their new-found skills and, further on, the girl from Kazan playing intently under a tree. The new Jerusalem which the Elm-hirsts founded all those years ago has borne wonderful fruit.