Proms 2012: Pélleas et Mélisande, Royal Albert Hall, review England and London, real and imagined, were the focus of the first two of this season's Proms. For the third, we were whisked away to the mystical, hazy kingdom of Allemonde, dreamt up by the Belgian symbolist playwright Maurice Maeterlinck and wrapped by Debussy in music of the most exquisite, enigmatic beauty. With John Eliot Gardiner conducting his Orchestre Révolutionnaire et Romantique, it was also a rare opportunity to hear the composer given the period- instrument treatment. Such a practice is arguably subject to a law of diminishing returns: revelations become fewer the nearer the repertoire comes, chronologically speaking, to our own era. But the telling variations in timbre were there, and Debussy's indecently beguiling 1902 score came across as subtly re-upholstered: the strings, with judiciously rationed vibrato, took on a light, waxy sheen, and the brass a mellow vulnerability; the clarinets sounded more caressing, the bassoons relaxed and reedy. With wind instruments tucked into the sides of the string section rather than ranged behind, the sound was beautifully integrated. The performance, marking Debussy's 150th birthday, also featured an outstanding, mainly French cast, many of whom had featured in a 2010 Paris production conducted by Gardiner. They moved fluidly around the orchestra, while an armchair and chaise longue at the front of the platform were the only concessions to any sort of staging. Laurent Naouri's gravitas and intensity emphasized the fact that Golaud, Mélisande's melancholy husband, is the opera's central character, often impotently rooted to the armchair here, rising occasionally to fearsome, helpless rage. Karen Vourc'h was an enchanting Mélisande, delicate but ample-voiced, whose song at the start of Act 3, delivered from the behind the orchestra, was mesmerising. The Canadian baritone Phillip Addis brought an ideally clean, youthful voice to Pélleas, and acted with a touching, wide-eyed innocence. Dima Bawab was disarming as the child Yniold, Elodie Méchain a rich-voiced Geneviève. More problematic was John Tomlinson's Arkel. The great bass's voice is still commanding, and the stage presence noble; but the raggedness on higher notes now, I fear, verges on the unacceptable. Ultimately, though, this was a showcase for Debussy's score and Gardiner's terrific orchestra, which between them conjured up more atmosphere than any staging ever could. Gardiner's conducting brought out the best in both, too, defined by urgency, clarity and an instinctive feel for inner drama. Most unpatriotic of him: he persuaded us, for one night at least, of French music's nonchalant superiority.