Concert performances of opera have always provided the international festival with some of its most memorable evenings, and this version of Mozart's great examination of the moral implications of absolute monarchy was no exception. It did, however, highlight one of the format's occasional problems, namely that fine individual interpretations - derived, one suspects, from stagings elsewhere - sometimes don't quite cohere into a satisfactory whole.

In this instance, there was something of a clash in dramatic approaches between Hillevi Martinpelto's Vitellia and Magdalena Kozena's Sesto. Martinpelto, mindful of the work's origins in classical theatre, was well-nigh Racinian in her combination of hauteur and telling restraint, with the slightest of gestures telling us all we needed to know about Vitellia's private hell. Kozena, meanwhile, portrayed Sesto as a neurotic figure, uncontrollable from the off. Both sang wonderfully, with Kozena's piercingly sweet tones contrasting with Martinpelto's richer voice, though occasionally one lost sight of the complexity of the couple's relationship. Presenting Sesto as essentially bonkers allowed Kozena little room for interpretative manoeuvre in the second act. Mozart suits Martinpelto far more than the downtrodden German Romantic virgins she has offered us of late, and she should sing his music more often.

Rainer Trost, replacing Ian Bostridge, was an exceptional Tito, voicing his arias with a combination of noble beauty and strength, subtly aware, unlike most interpreters, that compassion need not preclude toughness or fury. Christine Rice and Lisa Milne were exquisite as Annio and Servilia. The conductor was Charles Mackerras, second to none as a Mozartian and astonishing in his delineation of a world in which the pomp of imperialism hides the personal agonies that can destroy lives.