As things turned out, that first concert in 1968 gave little sense of the direction the Sinfonietta would eventually pursue, but it had impact: The main item being the auspicious premiere of a raucously anarchic oratorio by John Tavener called “The Whale.”
“I’d been at school with Tavener,” Mr. Snowman said, “and knew about this piece he’d written for the Bach Choir — who didn’t want it, for perhaps obvious reasons. So I suggested it to Atherton, and he said, ‘Why not?’
“That’s how we went about things then. There was no policy, no business plan — we just went for what we thought interesting.”
“The Whale” proved an overnight sensation, making Tavener’s name and that of the Sinfonietta in a single strike. William Glock, the august controller of music at the BBC who believed in giving listeners not what they liked already but (as he insisted) “what they will like tomorrow,” immediately offered it a second performance in Royal Albert Hall during the Proms, one of the world’s largest classical music festivals. The Beatles also took an interest, wanting to record it for their otherwise pop-oriented Apple label.
Mr. Snowman took an active role in the recording sessions. “Among the paraphernalia the piece required, like amplified metronomes and football rattles, was a phalanx of loudhailers,” he said. “I played one, my dad another. On a third was Ringo Starr.”
Credit via London Sinfonietta Archive
After this racy start, the Sinfonietta found its true métier with the arrival of Pierre Boulez. Mr. Boulez was in conflict with the French Ministry of Culture and refusing to conduct any orchestras in his native France. Instead, he started working with the Sinfonietta, leading major European tours from 1971 that pulled in other stars of contemporary music, including the Italian composer Luciano Berio.
“Then the penny dropped,” Mr. Snowman said. “I realized that with big names like that we could get engagements anywhere. And the money we earned abroad — which seemed to fall from the trees in those days — would pay for otherwise unaffordable projects here in Britain.”
The ensemble’s chief executive, Andrew Burke, looks back on the past 50 years as a history of rising standards in performance. “From the start,” he said, “we were a pool of solo-status virtuosi: a core group of around 16 players who were the best — and not just the best at contemporary music but across all genres.”
“The Sinfonietta,” Mr. Burke added, “raised the bar for what could be achieved in terms of technical performance — then went on raising it.”
This remains true, although half a century later other elite new-music bands are jumping over those once barely surmountable bars. Most of them, like the Ensemble Intercomporain, Ensemble Modern or Klangforum Wien, were created in the Sinfonietta’s image.
“We’re not the only act in town any more,” Mr. Burke said. “We have competition, but that’s to be celebrated. The other ensembles are part of our legacy. If they didn’t exist, there would be serious questions about what our relevance has been.”
Credit Claudia Greco
There may be other questions about the Sinfonietta’s record of achievement in persuading audiences to love some of the tougher sounds that it has championed in the past. But its choice of repertoire has never been a hard-line one. The Boulez and Xenakis have always been tempered with the softer voices of John Adams or Steve Reich. Indeed, Henryk Gorecki’s Symphony No. 3 became an easy-listening hit when the Sinfonietta recorded it in 1991.
The Sinfonietta’s repertoire now reflects the anything-goes pluralism of a music scene that stretches beyond concert halls into the kind of clubs where rock, pop and experimental music freely coexist. The current season takes in improvisation workshops, a collaboration with the photographer Andreas Gursky, and a piece described as a “politically charged multimedia game show” in which the composer Philip Venables invites the audience to question their ideas about gender.
More conventional, although it takes place in a disused printing plant rather than a theater, is the premiere of “The Cave,” an opera by the British composer Tansy Davies. She said in an interview that she loved the Sinfonietta for “their fearlessness, their readiness to shred a piece, if that’s what it requires, with heavy-metal energy.”
And there’s a conscious focus on the work of women, with premieres from Charlotte Bray, Unsuk Chin and Rebecca Saunders: three different voices ranging from the tuneful to the tough.
“Our sole criterion in programming,” Mr. Burke said, “is whether we believe a piece is good.”
It’s not for nothing is the Sinfonietta’s anniversary season is running with the tag “Unfinished business.”