Isserlis/Meta4/Fliter/ Festival Academy soloists, Cheltenham Festival, Cheltenham

Last year an unknown set of Mendelssohn variations for cello and piano came to light, but with the cello part missing. The pianist who found them commissioned a reconstruction of that part from an Italian composer; invited to premiere it, the British cellist Steven Isserlis confirmed that it sounded convincing. But it also emerged that the original might have been written by Mendelssohn's cellist friend Joseph Merk, who performed it with the composer at the piano.

"Variations spurieuses" was composer Tom Ades's apt comment – paraphrasing Mendelssohn's famous piano piece "Variations serieuses" – when shown the manuscript by Isserlis. At Cheltenham's Pump Room, courtesy of Isserlis and the Canadian pianist Connie Shih, we were invited to make our own judgments. Mine was that it's indeed convincing, but hardly a lost masterpiece. Even with the advocacy of this superb duo, it came over as a second-rate piece of froth, like many of this over-hyped composer's works.

The rest of the programme was outstanding, with pianist Shih displaying a brilliant talent for letting her soloist shine: I would love to hear her give a solo recital. The Cheltenham Music Festival is now well known for its innovative programming, and the other three concerts I attended were full of surprises. The first of these was a new quintet comprising the pianist Ingrid Fliter plus a young Finnish quartet called Meta4: in their hands, Schumann's Piano Quintet came over with unusual warmth. The day's two other premieres were impressive: Huw Watkins' "Four Inventions", inspired by a poem about the importance of empathy, had a Kurtagian charm; Michael Zev Gordon's "A Pebble in the Pond" was a fascinating realisation of a complex radiophonic work, much helped by Kit Hesketh-Harvey's gifts as a narrator. Sally Beamish's rumination on the Anglo-Saxon poem "The Seafarer" might have worked better without the projected charcoal drawings.

The day's triumph was an immaculate performance by the Festival's Academy Soloists of Schoenberg's "Verklarte Nacht" and of Judith Weir's Piano Quartet. A pellucid clarity of intention is what sets Weir's music apart: I could have listened to this spare, expressive work straight through again.

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