OPERA / Top of the pops: Meredith Oakes on Music Theatre London's playful Cos fan tutte at the Queen Elizabeth Hall

Most actors learn to sing a bit. When a winning, limelit Desdemona quavers through Shakespeare's Willow Song, or a gym-built hero picks up a lute and bleats out an embarrassing serenade, that's when you see what a gulf there is between real singing and brave, amateur tunefulness.

Understood in this context, the achievement of the actors who make up the small touring company, Music Theatre London, is remarkable: classic, strenuous operas sung at least personably all the way through.

At the Queen Elizabeth Hall on Monday, Mozart's Cos fan tutte was rescored by Tony Britten for violin, cello, two woodwind players, one horn and one all-purpose keyboard played by the conductor, Paul Bateman. Bouncy, playful, short-breathed, the music didn't float and soar as it can with an orchestra. But scoring like this was a more supple, fertile and sensitive compromise than the old-fashioned touring piano. And it was judiciously used as accomplice to the jokey modernity of the staging, as when the two disguised boyfriends, posing as redneck Americans, embarked on one of their courtship manoeuvres backed by a leering saxophone.

Stage energy was high, even if gesture and movement were pat. Jacinta Mulcahy, whose main work has been in musicals, sang both of Fiordiligi's big arias, sounding pleasanter than some operatic sopranos who attempt them. The newcomer Peter Corry was a reliably lyrical Guglielmo. Simon Butteriss struggled in the vocal toils of Ferrando but so do many full-time tenors.

The pay-off when actors perform an intricately constructed human comedy like Cos is in the physical immediacy and speed of the action. There were side-benefits one perhaps shouldn't mention, like the fact that both Fiordiligi and Dorabella (Mary Lincoln) were beautiful. Nick Broadhurst's production was conceived as a pert deployment of well-tried stage cunning. The men were RAF pilots, first seen behind the shiny, red shower curtains of their changing rooms at the base while Alfonso (Richard Hampton) jeered at them.

The girls were Gloucestershire types with a rag-rolled fitted kitchen. Their Ayckbournesque neighbour Despina (good mezzo Marilyn Cutts, irrepressibly omniscient in a floral jumpsuit) popped into it to make a consoling cup of coffee or offer a valium. Arias came translated in strange ways ('Life's a bitch and then you die') and the dialogue popped.

It all popped. I have to say I got thoroughly sick of its popping. I wanted the balm of a well-sung phrase. I wanted characters with fancies and ideals, not vulgar self-possession at every turn.

Mine was a minority view: most of the audience loved the whole thing. I overheard someone say in the interval: 'I should think it's infinitely more entertaining than the original, actually.' Ouch.

QEH, South Bank Centre SE1 (071-928 8800) To 1 Jan