The Royal Opera’s new production of Artaxerxes by the composer of “Rule Britannia”, produced in the Linbury Studio, is a delight. Long-forgotten works can often turn out to be a disappointment but this one’s a treasure. And a national one at that.

Thomas Arne had strong associations, not just with London, but with Covent Garden specifically. Artaxerxes, his most successful opera, was performed on the site of the Royal Opera House some 111 times in the three decades following its 1762 premiere.

Its subsequent neglect was less to do with disinterest and more a conflagration which consumed key parts of the score in 1808. It did carry on in the repertoire for another couple of dozen years but in a cobbled-together recreation and it’s been a labour of love by conductor Ian Page and his associates to get it back into a workable shape. Page has provided the missing recitatives and he gave Duncan Druce the task of setting the lost finale.

They have brilliantly excavated the once glittering garment, mended the holes, trimmed the frayed edges, taken it in a bit and now wear it once more with pride. Director Martin Duncan gives it a splendid production, with fabulous designs, tinged with orientalism, by Johan Engels. The wildly extravagant costumes are a wonder, forcing the singers into highly-stylised movement. A quartet of dark, faceless figures, lurk, shadow and push people into position, like Japanese puppeteers, and Duncan pitches the level of stylisation just right.

Arne’s music is never less than pleasurable and in places quite inspired. A folksy tang to some numbers cast us back to the slightly earlier Beggar’s Opera. Eschewing the da capo convention, the numbers never out-stay their welcome. We may be constantly reminded of Handel, but it’s actually closer to the opera seria style of Mozart – the juvenile Mitridate and even the mature Clemenza di Tito are continual reference points.

The plot is hardly worth dwelling upon, suffice to say it’s about treachery, loyalty and friendship amongst Persian royalty. There are plenty of opportunities for vocal virtuosity: Elizabeth Watts’ Mandane fires off exquisite fireworks in all directions and the other feisty female character, Rebecca Bottone’s lighter-toned Semira, dazzles similarly.

The trouser role of Arbaces gets some of the best material and mezzo Caitlin Hulcup, an impressive stand-in for Angelika Kirchschlager as Ariodante at the Barbican a couple of season ago, excels. The castrato title character is surprisingly less showy (maybe the dramatic similarity to Mozart’s Tito makes him less compelling) but Christopher Ainslie gives it his all, while tenor Andrew Staples is all malevolence and bright tone as the evil Artabanes. Steven Ebel is a rich-hued presence as baddie No.2.

Page nimbly conducts the period instruments of the excellent orchestra of the Classical Opera Company. Soloists – clarinets, trumpets, drums – are sometimes plucked from the yawning pit and placed on stage for added effect.

This is an evening that glitters and sparkles in all sorts of ways. It’s no wonder Haydn allegedly said he “had no idea we had such an opera in the English language.” Marking Thomas Arne’s 300th birthday, it’s a must-see for anyone interested in baroque (going on classical) rarities.