Rachel Nicholls was only brought in as a late replacement when Emily Magee withdrew after three weeks of rehearsal. You’d never know it. She and Heldentenor Torsten Kerl complement each other with unforced vocal beauty: they sing the score with a complete absence of excess baggage. There is no squall or big vibrato or weighty ‘monster’ singing, just unflagging power and, where needed, reserves of volume produced with astonishing clarity. Christian Thielemann recently described Wagner’s characters as “a crazy couple hovering on the verge of what is humanly possible”, but these two take it in their stride.

Kerl, despite a tendency to screw his eyes into a snarl during the big moments, brings lyrical sweetness and pathos to his role; Nicholls marks her ascent to the Wagnerian top table with singing of a limpid ecstasy that recalls Margaret Price in the Carlos Kleiber recording (although Isolde was a role Price never dared assume in live performance). Their erotic duet in the second act is ineffably moving – a highlight of the year in music.