From the off, this was something very special: Lothar Koenigs left the first, hypnotic phrase of the Prelude hanging in the late-afternoon air for so long that a literally ‘edge-of-the-seat’ frisson rippled round the theatre. For the next five hours, the tensions barely let up: sounding like a candidate for the Bad Sex Writing Award is something of an occupational hazard when writing about this music, but suffice it to say that every build-up was strung out to breaking-point, every climax delivered with searing power and the promise of more in reserve. Koenigs has already established himself as a Wagnerian of note with last year’s Meistersinger, but by the end of the evening I was willing someone to let him loose in the recording-studio with this music for the Wagner centenary. (My spellbound companion was hearing the score for the first time, and what a way to do so!)

We were tipped off as we collected our tickets that the Danish Isolde, Ann Petersen, was suffering from such severe hay fever that a cover had been flown in that morning, but her coruscating performance betrayed no evidence of vocal problems. Regal of voice and appearance, she captured the Irish princess’s volatility from her opening phrase, hurling out consistently beautiful top notes and conveying Isolde’s obsessive chemistry with Tristan long before knocking back the potion. Sadly, after the long interval we were told that her cords were so inflamed that she was unable to continue, and Anna Katharina Bauer sang the remainder of the performance (Petersen had clearly quit while she was well ahead, as the treacherous latter stretches of the liebesnacht had brought some of her finest singing yet). Bauer’s striking vocal and physical similarity to her predecessor made the substitution far less jarring than it could have been: her tone was perhaps not so opulent, but the slight edginess of timbre vanished for a properly hypnotic liebestod. Susan Bickley’s Brangaene, too, was a revelation: I’ve only heard this singer in lower-lying roles (principally Handel) before, but on this showing she’s a formidable hochdramatische, and sure to make a blistering Ortrud for the company in the autumn.

But for me, the main event of the evening was the return-to-form of Ben Heppner as Tristan. Now well into his fifties, the Canadian heldentenor seemed to be on the wane of late after several decades as the top international choice for some of the most taxing dramatic roles in the repertoire (a recent Peter Grimes at Covent Garden sounded rather frayed, as did Act Two of Tristan at the 2010 Proms), but on the evidence of this performance there are still few who can touch him in this role. He began tentatively enough (though in fairness Tristan’s diffident, offhand first scene offers relatively little opportunity to make an impact), and there were a few under-the-note phrases in the lead-up to the love-duet proper, but the stupendous third act brought some of the most thrilling live singing I think I’ve ever heard. Catching every nuance of Tristan’s delirium with mesmerising clarity, he hurled out the endless high Gs and A with near-superhuman stamina (it says much that Koenigs was able to let the orchestra completely off the leash here) and any sense of struggle was entirely dramatic rather than technical. Philip Joll’s Kurwenal, bluffly one-dimensional in the first act, worked wonderfully with Heppner here: his struggles first to reassure, and then to gently disillusion his master were extremely moving. Matthew Best made King Mark’s lengthy ‘I’m not angry, just disappointed’ monologue far more compelling than it sometimes can be, and Simon Crossley Buttle plangent Sailor and involved Shepherd will linger in the memory.

In summary, I very much doubt you’d hear a better Tristan anywhere at the moment – catch it (and especially Mr Heppner’s apparent Indian summer) while you can.

- Katherine Cooper