Two Proms premieres on successive nights, both cheered by capacity crowds, demonstrated how successfully some composers are dispelling the notion that all modern orchestral music is impenetrable when not plain nasty.

Admittedly, one of the pieces - New Era Dance, by Aaron Jay Kernis - is just a six-minute explosion of New York exuberance. Imagine the dances from Bernstein’s West Side Story rewritten for the rap era, with added sirens, gunshots, thunderous riffs - and a political agenda, because Kernis describes the 1992 work, pretentiously, as a plea for “political and social change” in the United States. (A third of the audience tittered, a third clapped, and the rest sat in stony silence when Mark Elder, the conductor, announced this from the platform.) No matter; it made a gloriously crazy start to the National Youth Orchestra’s Prom. And this huge ensemble, 160 players, went on to give a feisty account of Shostakovich’s Leningrad Symphony - that wartime blast of defiance, by turns banal, baleful and barnstorming. Electrifying passion, despite some shaky nerves.

But the Kernis pales beside the mesmerising piece played by the BBC Symphony Orchestra under Semyon Bychkov the previous evening. This was Magnus Lindberg’s Clarinet Concerto, which - if there’s any justice - will soon be as oft-performed as Mozart’s concerto.

Mind you, I shall count myself very clarinetically blessed if I hear anyone else play it with the astounding virtuosity and inventive genius of Kari Kriikku, for whom it was written. And I write “inventive” because at the work’s heart is a cadenza in which the soloist is given responsibility for summing up. Kriikku did that with such sublime deftness - and at the very limit of what was playable and audible - that 5,000 people let out a collective gasp.

That cadenza, however, was just one delight among many. With its fluttering solo line (full of multiphonics and other special effects), elfin fanfares, birdlike woodwind textures and shimmering strings, the piece seems to fly us giddily through an enchanted forest of bewitching sounds. But it also goes from A to Z cogently and transparently. The simple folk-like phrases of the opening grow to a “big tune”, before melting, like Prospero’s magic isle, into thin air. A perfect concerto, perfectly performed.

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