In the early 1970s, the anti-establishment Hips - the purveyors of Historically Informed Performance - opened ears to a whole new sound-world of gut strings and gut instincts about historical authenticity. But as with all stylistic revolutions, yesterday's avant-garde has become the new orthodoxy. With the exception of the occasional choral-society Messiah, you will not hear a professional, all-Handel programme - such as this mixture of miscellaneous arias with all three suites of Water Music - performed on anything other than period instruments.

Much has happened in the intervening quarter-century: instrumental technique has improved, intonation has evened out and Christopher Hogwood, doyen of Hip, has gone grey. But whereas most 1970s throwbacks are embarrassing, Hogwood accrues further degrees of dignity. The same goes for Emma Kirkby's voice. She is the star of early-music vocal style, and thanks to her career-long avoidance of large orchestras and auditoriums, her small but perfectly formed instrument has been kept in a miraculous state of preservation.

There is genuinely something timeless about Kirkby. She looks like a 19th-century painting, while the transparency of her vocal colour and her attention to the tiniest details amount to a unique manner of Pre-Raphaelite singing. Her account of the aria Sweet Bird, from Handel's pastoral masterpiece L'Allegro, il Penseroso ed il Moderato, was a transcendent piece of tone poetry, in which Kirkby and her obbligatist, Rachel Brown on baroque flute, warbled soft, avian impressions to each other from either side of the stage.

Unfortunately Kirkby's contributions were diluted by too much Water Music. A routine trot through some of Handel's most four-square incidental tunes is one of the least persuasive arguments for the continuing vitality of the period-instrument movement. Hogwood made his discoveries in this repertoire long ago. Most of the arguments have been won: this was mere repetition.