An authentic student orchestra created as a musical experiment by their teacher, the English composer Gavin Bryars.
Bryars encouraged absolutely anyone to join, regardless of their musical ability. If you could play an instrument you had to switch to one you couldnt, and everybody had to try as hard as they could; trying to play even slightly badly on purpose was verboten. The orchestra attracted a great deal of media attention, which mostly focussed on their hilarious sound, but which nevertheless led to singles, albums, and even a film.
And there was a method to their madness. The Sinfonias early works were drawn from standard classical touchstones (The Blue Danube waltz, The William Tell Overture, etc) so most orchestra members at least had a vague idea of what the piece should sound like. Even if they couldnt play their instrument at all they would still know when to go high and when to go low, the end result being the whole ensemble playing not only the correct note but also several notes nearby - clouds of sound that gave an average impression of the piece.
This interested many avante-garde musicians, to the point where Brian Eno actually joined, playing the clarinet and producing their first two albums.
Although they never officially disbanded, they havent played together since 1979. Their final impact on popular culture before now was this 1981 top 40 single, a medley set to a disco beat that was their attempt to cash-in on the vogue for Hooked on Classics