The most memorable part of this concert was unprogrammed. The London Sinfonietta’s superb principal flute, Sebastian Bell, was a permanent fixture in this pioneering ensemble from its foundation in 1968. He was playing up to his death 12 days ago. So Monday’s concert began with an eloquent tribute by John Constable, and then a performance of Autre fois, a suitably elegiac piece for flute, clarinet and harp by Berio.

But the show must go on. This concert, conducted by Diego Masson, launched the Southbank’s Luigi Nono festival – a sprawling tribute to the Italian composer who died in 1990, culminating next May in the British premiere of his massive epic, Prometeo. I hope that is more gripping than the pieces presented here.

First up was Incontri – “encounters” between abrasive brass bursts and sustained string clusters. The latter seemed to strive towards ethereal realms, while the former remained earthbound. But that seemed very little to glean in seven minutes.

Then, after a fine performance of Schoenberg’s Chamber Symphony No 1, came some early Nono: the 1950 Variationi canoniche based on a note-row in the Ode to Napoleon by Schoenberg, whose daughter Nono married. I loved the start – wispy fragments, exquisitely orchestrated. And I loved the nostalgic polyphony that emerges later. But of the bizarre central section – seemingly unrelated bangs and biffs – I could make neither head nor tail. I wonder what Schoenberg thought of his son-in-law.

Finally came No hay caminos, hay que caminar . . . Andrej Tarkovskij. Nono’s 1987 tribute to the Russian film director takes its title from an inscription in a monastery: “Pilgrim, there is no pathway, there is only travelling itself”. That stern message is the essence of the score. It deploys its forces in spectacular, 17th-century Venetian antiphonal style. But the music itself laboriously unfolds tiny events: single-note crashes, patterings on distant drums, long-held dissonant drones. Fascinating for connoisseurs of the postwar European avant-garde – but I doubt if the wider public is ready to say “yes, yes!” to Nono.

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