Tristan und Isolde/BBC Symphony Orchestra, Barbican Hall, London<br></br>Dorothea Röschmann/ Stephen Loges, Wigmore Hall, London<br></br>Ian Pace, Jerwood Space, London

Under the duvet with Tristan, Isolde and... Donald Runnicles

So she looks like a well-to-do medium and he looks like an undertaker with a rock'n'roll past? So they're neither of them young or, in this necessarily static series of concert performances, noticeably restless? The coupling of soprano Christine Brewer and tenor John Treleaven in the BBC Symphony Orchestra's electric, episodic account of Tristan und Isolde under Donald Runnicles at the Barbican is still as erotically persuasive a musical partnership as any more lissom or lively duo I've seen on stage.

In much the same way as at the start of this series last December, the brilliance of Act II of Runnicles's Tristan rendered the concert's first half – Strauss's fidgety, overblown elegy Metamorphosen – redundant. Once again, that first half showed less the influence of Tristan on later composers than a parlous lack of rehearsal-time; highlighting the technical weaknesses in what is now proving an excitingly unpredictable orchestra. Once again, the orchestra that went on to play the Wagner was an orchestra transformed in blend, attack, discipline, expressivity, and dynamic and textural range; not just from their performance of the previous work but from any of their performances I can recall bar the first in this series. Galvanised barely covers it.

If Runnicles, who is rarely seen on these shores, has yet to prove to his Barbican audience what he can do with composers other than Wagner – December's Debussy was as amorphous as this week's Strauss – he has proved beyond a doubt that it is possible to combine extreme sensuality with literary awareness. (An elusive combination in a work that is oftentimes either icily cerebral or sweatily hormonal in performance.) Certainly he is aided by Dagmar Peckova's complex, copper-toned Brangäne and Brewer's voluptuous, dazzlingly easy and unmistakably intelligent reading of Isolde. But in an ostensibly land-logged act, where the watery turbulence of Act I's voyage becomes a tempest of frustration and convulsive desire, it takes serious control to lift the duvet delicately enough to allow consideration of the tiniest lyrical nuance. The orchestral shimmer around Isolde's fascinated murmur "das Wortchen 'und'" was breathtaking: such a simple word, "and", yet for these lovers a word that means certain death. More impressive still – though the acid test of this will come later this month when the opera is broadcast on Radio 3 over three consecutive evenings – is the way in which Runnicles makes the thematic amplification of each act feel so utterly cohesive within the larger structure of the work. With Treleaven's stiffly crimped vibrato of Act I now smoothed into a lean, steely yawn of sound and the BBCSO reshaped into a darkly suggestive, organic unit, Act III promises to be unmissable.

Rather like Simon Keenlyside and Dorothea Röschmann's recital of Wolf's Mörike Lieder with pianist Malcolm Martineau at the Wigmore Hall last Sunday promised to be – until "unforeseen circumstances" intervened and Keenlyside withdrew from the performance. Now, full marks for bravery to Keenlyside's last minute replacement, young baritone Stephan Loges. His is an attractive voice and one that shows signs of growing into a sizeable, handsome instrument. But Loges is still learning how to use it to best effect – sidling hesitantly around his own sound like a nervous rider attempting to mount a feisty thoroughbred – and the polite, scholastic style in which he sings Schumann or Bach has yet to display sufficient complexity, control or moral ambiguity to translate the erratic charms of Wolf.

Am I blaming one young singer for an unexpectedly limp duo recital? Not a bit of it. The main problem with both Loges's and Röschmann's performances – though the latter improved greatly in Rat einer Alten and the spectacularly creepy Erstes Liebeslied eines Mädchens – was their mystifying deference to Martineau, whose peculiarly paced, fuzzily executed and only notionally characterised accompaniment showed all the signs of his having lived with this repertoire for years without having aimed for anything deeper than flat wit and technical aptitude. Ah, but Wolf is difficult music, I hear you say. Quite so. But the contrast with Andrew West's alert interpretation of the West-östlicher Divan accompaniments in Mark Padmore's recital at the same hall last month was a sharp one indeed. Perhaps it boils down to the peculiar protocol between singer and accompanist? (A partnership that should be equal but that in practice is rarely so.) Perhaps it's simply a matter of experienced accompanists giving younger singers "permission" to impose their own personalities? Then again, perhaps it's just down to practice.

Which leaves barely a minute to acknowledge Ian Pace's brilliantly lucid performance of Sir Peter Maxwell Davies's somewhat less lucid 1955 work, Five pieces for piano – a Debussian pre-echo of the 1957 out-takes from Thelonius Monk's Round Midnight – at the 60th birthday party of the Society for the Promotion of New Music. To maintain such concentration against a background hum of "Which number is this?", the continual sigh of uncorked bottles, and the scritch-scratch of one thirsty commentator's mid-performance ballpoint and paper-tablecloth graffito "Still Playing Naff Max" – not me! – is quite a feat. SPNM's anniversary celebrations carry on all year with concerts aplenty, so for now I'll simply wish them many happy returns.

a.picard@independent.co.uk

BBC Symphony Orchestra's 'Tristan' series concludes at the Barbican, London EC2 (020 7638 8891) 19 February and on Radio 3. Acts I and II are broadcast on 17 & 18 Feb