Faultless choral singing in the tiny Ave verum corpus, taken at a flowing (and palpably two-to-the-bar) tempo, augurs well for a Requiem of power and intensity. So too does Marie Lys’s scintillating dispatch of both the cantilena and the coloratura of the motet Exsultate, jubilate.

John Nelson, most readily identified with the music of Berlioz, proves himself an instinctive Mozartian, as sensitive to the delicacy of the composer’s orchestration as he is responsive to the drama of his sacred masterpiece. From the solemn tread of the opening ‘Requiem aeternam’ to the grandeur of the ‘Rex tremendae’ and the fevered contrapuntal invention of the fugues at ‘Kyrie’, ‘Quam olim’ and elsewhere, his tempos are always apposite and his balancing of the disparate forces – soloists, chorus and dark-hued orchestra – precise and perceptive. The accuracy of the performance is uncanny, given that all three pieces were recorded in concert (presented without applause).

This isn’t, though, the traditional version of the Requiem. The German composer and musicologist Michael Ostrzyga has revised the orchestration of the Sequence (from ‘Dies irae’ onwards) and Offertory, and reimagined the succeeding movements, for which no material in Mozart’s hand survives. Benefits include the clarification of the counterpoint in the ‘Recordare’, of which Süssmayr made an almighty hash, and more appropriate instrumentation elsewhere; listeners will also spot occasional string lines transferred ear-tweakingly to woodwinds or vice versa, and brass and drums in unexpected places.

Ostrzyga’s interventions go far further later on, though. Although Nelson has not opted for his redesigned ‘Lacrymosa’ and amplified ‘Amen’ fugue, the Sanctus and Benedictus are both considerably recomposed; and, in order that the ‘Osanna’ fugue be heard in the same key after both movements, Ostrzyga contrives a modulation at the end of the B flat Benedictus back to the D major of the Sanctus – a radical divergence from the familiar version. The Agnus Dei, too, follows a reimagined harmonic trajectory.

Readers may remember an earlier recording of Ostrzyga’s edition from Concerto Köln. That version followed another path through his edition (published last year by Bärenreiter), choosing different options where more than one alternative was presented: that ‘Amen’ fugue, for instance, and a startling minor-key Sanctus. For those who are excited by such interventionist responses to Mozart’s fragmentary score, Nelson’s recording can be recommended alongside Helgath’s; it’s certainly the finer performance in its own right. But be aware: it’s a strikingly different and not unchallenging departure from the Requiem we all know and love.