So now we know. There isn’t an overlooked masterpiece lurking in the dusty annals of 18th-century English opera. Not by Thomas Arne, anyway. Resuscitated on the site where it was premiered 247 years ago, his Artaxerxes proves to be a competently crafted work full of dapper little tunes (28 numbers, many lasting less than 90 seconds) and dab touches of orchestration — including clarinets, which must have been a novelty in 1760s London.

But place it in its historical context and its grand-opera limitations are apparent. It lacks Handel’s heroic passions, Gluck’s noble purposefulness or Mozart’s wit. Arne clearly had a great facility for producing ingratiating ballad-opera melodies. The trouble is that this story — of a son stitched up by his own father, a general who has murdered the Persian emperor Xerxes — cries out for deeper treatment than he can give it. Time and again an aria begins well, promising to convey fully the emotions of the character singing it, but then some bland cadence or hackneyed sequence cheapens its effect.

Still, if you see Artaxerxes only once in your life (and once is enough), see this cast in this production — jointly mounted, in a slightly premature celebration of the 300th anniversary of Arne’s birth in 1710, by the Royal Opera and the Classical Opera Company. For a start, it looks ravishing. Martin Duncan’s staging uses nothing except costumes, screens, masked mimes and one amazing, gold-armoured imperial statue. But the costumes (Johan Engels) are fabulously embroidered on 18th-century “oriental” lines. This period feel is matched by clever use of a ribbon stage in front of the fine period-instrument orchestra, so that the singers can get up close and personal with the audience as they emote their fears or fury.

They emote well, too. The Australian mezzo Caitlin Hulcup’s occasional British appearances never fail to impress, and here she excels as the wronged son Arbaces, stoically loyal to his dastardly dad (Andrew Staples, with a sneering curl of the lip to match his commanding tenor). The countertenor Christopher Ainslie is dignified as Artaxerxes, bemused heir to the murdered Xerxes; and Rebecca Bottone splendidly spirited as his lover Semira. But the pick of the bunch is Elizabeth Watts, who musters buckets of passion and thrilling coloratura as Xerxes’s anguished daughter Mandane.

A punchier conductor than the genteel Ian Page might haul more of Arne’s arias out of their teashop cosiness. But credit to Page for reconstructing the missing recitatives (superbly accompanied, with prodigious dollops of double-stopping, by the cellist Joseph Crouch) and Duncan Druce for composing music for the lost finale. The only problem is that it sounds too imaginative to be Arne.

To Nov 14. Box office: 020-7304 4000

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