Four patients, each with a different ailment, languish in a run-down hospital, where they have been treated by a succession of overpaid, overprescribing incompetent quacks. Waiting times are interminable, treatment is expensive. The politicians have to get involved. A new doctor arrives, who is not all that he seems, and then things start getting truly surreal.

This all sounds like a newly written opera about the NHS, but it isn’t: l’Ospedale is a 350 year old piece from the very early days of opera, lovingly exhumed from the archives by Goldsmiths lecturer Naomi Matsumoto and moulded into some kind of stageable shape by conductor James Halliday, baritone Jonathan Sells (who sings the doctor) and their “Solomon’s Knot Baroque collective”. The result is an hour of delectable light operatic entertainment.

The venue, Wilton’s Music Hall, is also being lovingly restored: it's a genuine Victorian music hall in an enclave of old world London close to the Tower, with a couple of hundred seats (reduced for this production), an ornate gallery, high ceilings and bags of character. The original stage is set high above floor level: in this production, it contains the musicians, surrounded by orange plastic bin liners with the personal effects of countless patients (most of them probably deceased). James Hurley sets the action at floor level where the stalls would normally be, in a simple set with a curtained hospital bed, a rusty wheelchair and far too many neglected urine samples.

The music, by an unknown composer, has the typical characteristics of pre-Baroque opera: it's lively, tuneful and energetic, always making you want to get out of your seat and dance. James Halliday and half a dozen musicians bring it to life wonderfully, with the combination of lute and guitar especially prominent. To bring some contrasting pathos to proceedings, a couple of madrigals are thrown into the mix, and these turn out to be the musical highlights of the evening, with magical voices which blend beautifully in the warm acoustic of Wilton's. Inevitably, it's the high voices that catch the ear, with flowing lines that soar above the others: soprano Rebecca Moon and countertenor Michal Czerniawski. 

Antonio Abati's libretto is exuberantly wacky and an uncanny demonstration that some things don't change over the centuries: the patients conditions being lovesickness, anger management, neurosis and – the one condition that is completely incurable – absence of ready money. The Italian is amusing enough on its own, with some major liberties being taken in surtitle translation – sometimes just a little too knowing – to add spice for a 21st century audience. The spoken prologue and epilogue (in English) come over a PA from a distinctly David Cameron-like character (the phrase "big society" appears at least once) with a background of distinctly House-of-Commons-like sound effects. It's all good, riotous fun.

Really, this is an ensemble piece rather than a star vehicle. I'm going to eschew the normal reviewer's procedure of name-checking every voice, because that's not the point: the gags come thick and fast, the acting, directed by James Hurley, is excellent from everyone, and all of the voices are plenty good enough to fill the relatively small space with music written before the Handelian period in which opera started to be an exercise in how-virtuosic-can-you-get vocal pyrotechnics. 

L'Ospedale is a treat – a puff-pastry vol-au-vent of a piece. Go see it.