Iolanthe, Wilton's Music Hall, London

In the current phase of small-scale reassessment of musical-theatre masterpieces, the Gilbert and Sullivan revivals at the little Union Theatre in Southwark, with all-male casts and a solo piano, have gone slightly under-appreciated.

But first with The Pirates of Penzance, and now with Iolanthe, director Sasha Regan and her boys are doing something just as gloriously fresh and inventive as Matthew Bourne did with Swan Lake, or Richard Jones with Annie Get Your Gun at the Young Vic.

And it's not necessarily radical, in a "conceptual" or vindictive manner. Above all, it's not camp or knowing. Sentiment is pure and humour affectionate, which takes some doing with the slightly arch nature of the story, in which a stage full of fairies and peers squabble over the Victorian romance between a chap, Strephon, who is only a fairy "down to the waist" and a shepherdess who is a ward of Chancery. An all-male chorus of fairies are genuinely charming and funny in their improvised costumes of corsets, vests, cami-knickers and wings of bunting and silk strips.

Strephon's bid to wed Phyllis takes him into Parliament in order to wrest her from the competitive attentions of the peers and the Lord Chancellor himself. Meanwhile, the fairies begin to love the peers, and their Queen (played as a magnificent contralto by Alex Weatherhill) is persuaded to change fairy law so that fairies and mortals can mingle and procreate.

Gilbert's satire may have dates, but his wit and the pointed hilarity of expression certainly haven't, and Sullivan's endlessly inventive score is one of the most gorgeous in the whole G&S canon.

The falsetto singing is a joy, and Christopher Finn as Iolanthe, Strephon's fairy mother, achieves an astonishing mix of tenor and falsetto registers in his big second act number. If you still don't like G&S, this is the show to go and see.

To 7 May (020 7702 2789)