Though certainly known among cellists, the three Martinů cello sonatas don’t turn up on chamber music programmes with the frequency that they deserve, and not due to any compositional deficits. However, the airy, expansive Martinů heard in his symphonies is only glimpsed amid certain chord-voicings and harmonic progressions in these dense, heterogeneous works, bursting with ideas, maybe too many for their own good, sometimes knocking into each other, particularly in the piano-writing. Tonal centres don’t stay put for very long. Often a separate bitonal layer is in there. Only in the Third Sonata does one hear more codified, mainstream Martinů but that’s only because the use of simultaneous tonalities is more a source of spice and wit.

Or so it seems in these performances, which unapologetically don’t look back. Isserlis and Mustonen enjoy considerable chemistry and are so much in the moment that matters of continuity and architecture are mainly taken care of by their headlong momentum. Isserlis makes lower registers growl (especially apparent in the fine SACD sound). Mustonen relishes the interruptive qualities, the outbursts and abrupt changes of direction with a sonority that one might describe as aggressively crystalline. The one movement that’s more expansive than busy is the Second Sonata’s Andantino but Mustonen takes the music to a particularly anguished place, revealing it as some of the most singular music in all of Martinů’s considerable output. Though only four minutes long, it feels epic.

The three sonatas are separated by Mustonen’s own Sonata for cello and piano, dating from 2006, which, like Martinů, stands halfway down the road to modernism. There’s adventure here but the thematic material is unexceptional in ways that becomes more apparent on repeated hearings. Then there’s Sibelius’s curious Malinconia, Op 20, whose rather good moments are buried behind what sound like parodies of Saint Saëns and Chopin, with everything cut short by a whopping case of attention deficit disorder.

The Chandos disc by Paul and Huw Watkins takes a more balanced, lyrical view of Martinů’s sonatas and is filled out by the Variations on a Slovak Theme and Variations on a Theme of Rossini – not major works but a better counterpoint to the formidable music around it.