The Office: The Opera started out as a joke. Its composer, Anne Chmelewsky, decided to turn the saga of Wernham Hogg into an opera as a way to "take the piss" out of the stuffy classical music course she was taking at the Guildhall in 2006.

Given first permission and then encouragement by The Office's co-creator Stephen Merchant, Chmelewsky staged a clip of the opera for Comic Relief.

Now, again in aid of charity, comes this one-off in front of an amiably tipsy twentysomething crowd in a sweltering studio at the Proud Gallery in Camden.

The warm-up act is Tom "Red" Calvert - a human beatboxer of jawdropping prowess - who also plays Tim; and for an encore, Matthew Wright's David Brent does The Dance.

It's a bit studenty, perhaps. But Beyond The Fringe was studenty.

There's everything to be said for doing a joke if you do it properly, and this has been done with glorious care and attention.

My friend the opera singer, sitting in the row in front of me, confirmed what my tone-deaf ears were only able to suspect: "Really good singing." Good singing, good acting, good gags.

The physical comedy of the show was well mimicked - from Wright's nervous tie-stroking as Brent, to Tim's sardonic raised eyebrows and hangdog scratching behind the ears, as recreated by Calvert.

Dawn blushed the right shade; her fiancé Lee was appropriately oafish. Only Ezra Williams's Gareth - bearing no physical and scant gestural resemblance to Mackenzie Crook - seemed an import.

There's a lot in this production to indicate that The Office would work rather well as opera.

The characters have a sort of light-operatic archetypal vigour - Brent as a masterclass in braggadocio; his sidekick Gareth as a Malvolian malcontent, and the love of Tim for Dawn as just the stuff of which anguished mock-heroic arias are made.

But in its present form this is very obviously a squib rather than a fully formed and independent work.

It jumps from song to song, and from fragment of plot to fragment of plot, like an operatic sketch-show rather than a piece of work trying to tell a story.

And it doesn't so much end as stop, abruptly and without warning.

Mind you, the plots of most other operas are complete bollocks too.

This is funnier, and shorter, than Der Ring des Nibelungen. And Wagner never thought of putting a stapler in a jelly.