The task of a conductor and stage director, then, in Tristan, is to shape it like a roller-coaster, holding the long duets in the tension of a slow, focused ascent to that end-of-act peak only to plunge down and begin the upward crawl again; and it was superbly done by Mackerras and his director/designer Yannis Kokkos who between them have added another jewel to WNO's crown of world-class productions.
Mackerras's strength is the way he combines an unhectoring particularity of detail with clean phrasing and a sense of purpose that registers even at the slowest moments. Kokkos offers something similar, in strong but unemphatic imagery that tells the story with minimum fuss, maximum tension, against a background of abstracted sets that look like (and maybe are) solid sculptural installations. You can't tell which way the boat is going in Act I; but perhaps it isn't going anywhere. Perhaps the journey is internal. And perhaps it's no coincidence that what Wagner specifies as a curtain separating Tristan from Isolde in that first act becomes a gauze with the look of a prophylactic membrane, swiftly removed at the appropriate point. Safe sex is clearly lost on these lovers.
As for the voices - and Tristan ultimately stands or falls by them - this is a pearl of a cast. Anne Evans sings Isolde with a purity and integrity of intonation that compares with Margaret Price in her prime. The pitches are discernible, without the parrot-squall that audiences these days are encouraged to believe defines a Wagner voice. You hear behind it all the lyric quality of the lighter roles which launched her career - the Mimis and Countesses - and you wonder why we don't hear this wonderful, undervalued artist more often.
Her Tristan, Jeffrey Lawton, isn't built to react and doesn't; but he does have the vocal attributes of an uncommonly sophisticated Heldentenor, shading the dynamic with a fine pianissimo that throws the big statements into proper relief. And there is impressive support from Della Jones's Brangane and Richard Paul Fink as Kurwenal. Collectively they make a remarkable show - to be caught at all costs as it tours through the coming months, arriving at Covent Garden in April.
There is still, just, a chance to catch the equally remarkable, staged St Matthew Passion which opened on Thursday at Holy Trinity Church, Sloane Street, and is quite simply one of the best offbeam ideas I've ever seen translated into performance. When it was first announced, I was sceptical. There is no good historical precedent for staging the Bach Passions (quite the opposite), and if it had to be done, the St John Passion seemed a better choice as the more conventionally dramatic of the two. But conventional drama isn't what Jonathan Miller, the stage director, is after; rather, an experiment in applied storytelling that exploits the repetitions in the Passion text to create an artifice of three-dimensionality, much as Harrison Birtwistle's operas do when they reconsider and recycle the same event from different angles.
Typically in the Passions the Evangelist tells you what Jesus is going to do, Jesus does it, and someone else reflects on it after the event in a way that divorces the narrative from historical time and gives it the tension of something caught between theatre and liturgy. What Miller does is amplify that tension with movement. But he does it with extreme economy: no sets, lighting or costumes, just an in-the-round space defined by a circle of performers (singers and instrumentalists together, in everyday clothes) and surrounded by the audience. The atmosphere is cramped, seething but focused, like a courtroom drama happening on a railway station in the rush hour, and electrifying. With no clear territorial division between performers and audience, it feels participatory; and because the singers itinerantly emerge from different parts of the crowd, you never know where to anticipate the sound source, which is of itself exciting.
Not that the singers have much stage business to do; and in the case of the 'abstract' soloists with no given character it's hard to know what they could do. Miller has them take a keen interest in the obbligato instruments accompanying them, which looks potentially odd but is done with absolute conviction by a committed cast of stars such as James Bowman and Nancy Argenta and a dynamic young double-chorus of 24 voices from which the lesser solo roles are drawn, as they would have been in Bach's time.
This does not, in fact, purport to be authentic period performance (Bach had no more than 12 voices all told, including Christ and Evangelist) but it uses period instruments, divided with the choirs antiphonally across the performing space in the way Bach would have grouped his forces around the two organ lofts at St Thomas's, Leipzig. And the conductor Paul Goodwin adheres to the autograph manuscript of 1736 rather than the usual patched-together editions, which means no boy trebles for the opening chorus.
There is, one has to say, some sacrifice of purely musical values in what happens. Performance in the round involves a loss of vocal continuity when singers turn their back to you; and the playing isn't always immaculate. But Rufus Muller's Evangelist is superb in its animated lyricism (far from the standard figure of passive condolence; when the narrative spits, he spits); there is an outstanding young tenor in Jamie MacDougall; and Goodwin is an inspiring conductor who delivers what is, overall, an extraordinary piece of work. The one regret is that more people won't see it, unless it goes on tour or gets on television. Either way, this Passion could be hot.
'Tristan': 6 March, 0222 394844. 'St Matthew Passion': tonight only, 071-730 1745.