Così fan tutte review – Phelim McDermott's fairground delights soon wear thin

Phelim McDermott's production of Così fan tutte has all the fun – and some of the disturbing sleaziness – of the fair. It starts with fairground figures pulling placards from a trunk as the overture unspools, announcing that an opera is about to commence: PLEASE CONCENTRATE! A SOPHISTICATED ANALYSIS OF MEN AND WOMEN IN TWO ACTS… BIG ARIAS… You get the playful, non-reverential, stubbornly original drift.

A motley crew assembles: sword-swallowers, fire-eaters, dwarves, a giant, a bearded lady. Tom Pye's seaside funfair with ferris wheel against a glowing sky makes a spectacular setting for the amorous carryings-on. And I've never before seen opera singers eating candyfloss on stage. McDermott has a nerve – that is his strength and, sometimes, his weakness.

As Don Alfonso, Roderick Williams inhabits his role as spivvy operator to perfection – the only scrupulous thing about him is his singing. The lovers Guglielmo (Marcus Farnsworth) and Ferrando (Randall Bills) sing splendidly but overreach their actorly limits with entertaining, but embarrassing, Elvis-style hip swivelling and thrusting as the second act's lewd lads. Dorabella (Christine Rice) and Fiordiligi (Kate Valentine) are a couple of lustful misses in 50s knitwear whose voices ring sumptuously true – although they mock love and themselves. Mary Bevan's tip-top Despina, from the Skyline motel, is a minx who has been there, kissed that and steals other people's hot chocolate. Conductor Ryan Wigglesworth keeps the musical show perkily on the road and the cast is wonderfully served by Jeremy Sams's flirtatious new translation.

But the difficulty the production creates is how to accommodate the points at which Mozart is not, musically, having a laugh. Lyrical beauty cannot expect to survive untarnished when nothing is straight, when almost everything comes with the equivalent of a nod or a wink, or from inside a spinning tea cup. A less affecting Così is hard to imagine, but by the second half, the fairground's delights are wearing thin. Fiordilgi sings her second act aria from what looks like a soup bowl attached to a balloon (at a point where she is far from morally buoyant). The soup bowl ascends pointlessly, then comes down. The evening follows suit.