Not given to routine planning, Steven Isserlis comes up here with a generous, characterful programme of early-Romantic masterworks—formerly B-road stuff, these days anything but—offset by two suspendingly beautiful song arrangements inimitably natural in their tessitura, utterly painful in their introspective longing. There's a forgotten little 6/8 Larghetto, too, by the dedicatee of Chopin’s Cello Sonata, Auguste Franchomme (1808-84), published in Leipzig in 1838, during the E-flat middle section of which Schubert, dead ten years, quietly dances the ether.

Isserlis approaches both main works expansively, getting his 1726 'Marquis de Corberon' Stradivarius to sing, project and fade with beauty, form and expression foremost. More than once one is struck by how paragraphs and episodes breathe, surge and cadence, rests and silences given potent tension; this is finely articulate cultured playing—ruminant poetry and reflective musicality, aristocratically suspended climaxes, carrying the argument free of ego or 'produced' theatre. Chopin's complex first movement, a ballade-like narrative difficult to hold together, particularly impresses, amounting in Isserlis's hands to perhaps the closest the composer ever got to sustaining a prolonged symphonic dynamic. It compels at every turn of its leisured fifteen-minute journey. Similarly one would not want to be without the gloriously poised aria of the Largo. The early Polonaise brillante goes with a Slavonic swagger, its imperial rhythms ideally placed, neither rushed nor laboured. Good polonaise playing, like good mazurka feeling, is an art not all have the key to.

In programme order, out of Chopin's later (1845 and same key) ‘Nie ma czego trzeba’ comes Schubert's 1824 Arpeggione Sonata (for a now-defunct instrument), unpublished until 1871, a bouquet of traceries and grace, its more strenuous passages benefitting from the openness of the keyboard writing. Repeatedly, Isserlis regales us, Schubert the Sonata man was one like no other—fashioning canvasses as dependent on sighing Lied contrasts and expanding caesuras as the pursuit of purely Beethovenian dialectics. In these pages strasse tunes and sparing motifs go hand-in-hand, uncontrived companions of the Biedermeier hour, lilting and tilting their way through time. Isserlis's 'song without words' Schubert is magical. And infinitely sad.

His booklet essay is wisely expressive reading. Likewise his note on the editions used. Most telling, in the Chopin Sonata, is his adoption of two autograph tempo markings otherwise ignored: Maestoso rather than Allegro moderato for the first movement, and Più lento for the Trio section of the Scherzo – both bringing needed air and space to the music. Apparently small changes, yet, as he says, 'these things make a difference…'.

Dénes Várjon is a gracious partner, maybe not always at home in Chopin's trickier figurations but otherwise agreeably in accord with Isserlis's wider vision. He plays an 1851 Érard (Birmingham University Music Department), tuned to A430. More opaque and less 'big' than expected (compared with examples we've heard in Paris or Warsaw), the lyric mezzo domain is where it speaks best, generating a warmly pedalled halo of overtones and breathtaking die-aways (the end of the Arpeggione for one, both song transcriptions for another). In denser, louder textures, though, it loses clarity and attack, the engineered balance with cello—picking up on an ambient acoustic prone to cloudiness— producing occasionally muddied artefacts.