Kate Bassett on Once: A song's less sweet, second time around

It was a film, then a Broadway hit. Now it's in the West End. But not all encores are welcome

One more time ... The multitasking, rollicking cast of Once in the on-stage bar (Geraint Lewis)

You can't reprise Once, can you? The title implies as much. Moreover, what rendered John Carney's original, award-winning, low-budget 2006 movie so extraordinary was that, while being at heart a romantic musical, it looked like docudrama, with close-up, handheld camerawork.

Two skint musicians – an Irish busker and a Czech single mother – meet on the unprettified streets of Dublin, fall for each other and join forces to make a storming studio recording, except they're still holding out for their old flames.

If you want to love the stage version, you're going to have to forget the authenticity and light touch of the film in which Carney's actor-musicians wrote the folk-rock songs themselves and improvised some of the dialogue. This heavily re-scripted adaptation, directed by John Tiffany, can't really match up. Did it merit the Tony Awards it landed in New York? Well, Enda Walsh's plonking rewrite adds lots of caricatured bit parts. He makes the protagonists spell everything out, and he mucks up the narrative pacing at the start. As the busker who's nursing a broken heart, Declan Bennett seems coldly self-absorbed, then suddenly on the pull. Zrinka Cvitesic, as the unnamed Girl, has too many bossy, didactic lines.

So this production takes a while to exert its charm, but it's hard to resist the entwined harmonies when Bennett and Cvitesic tentatively start to duet – on acoustic guitar and piano – with the ballad "Falling Slowly". She's a delicate beauty with an almost ghostly, floating voice, and he opens the emotional floodgates when he sings with raw yearning.

The rest of the cast multitask too, as actors, scene-shifters, and a rollicking band, launching a stomping ceilidh and occasionally slipping into expressionist dance moves (slightly underdeveloped by choreographer Steven Hoggett). You can even join in the craic, if you want, as the setting is an old pub with glowing wall lights and speckled, silvery mirrors. At the interval, this serves as an onstage bar where performers and punters can mingle.

Meanwhile, at the Barbican, the company Cheek by Jowl has boldly added handheld film footage to a notoriously anarchic play from the 1890s. This is Ubu Roi (***), Alfred Jarry's absurdist saga about a foul-mouthed usurper-tyrant and his wife – a piece more commonly staged with puppets or grotesque clowns.

Director Declan Donnellan's stage setting for this surtitled French production is a bland, modern living room, the table laid for a dinner party. The host and hostess (Christophe Grégoire and Camille Cayol) admire each other smoochily before the guests arrive. Curled on the sofa behind them, though, is her menacingly screwed-up adolescent son (Sylvain Levitte), a Generation Z Hamlet armed with an Oedipus complex and a camcorder which throws magnified images on the back wall. Prowling around, he zooms in on his parents' canoodling, on bloody joints of meat, on filth hidden in the shag pile, and on his own wolfish maw.

Then, as if compelled by the power of the boy's twisted imagination, Grégoire, Cayol and their simpering guests turn into the savage and rampaging monsters of Jarry's fantasy – first developed when the writer was himself a schoolboy.

Ultimately, even Donnellan's ingenuity and intelligence can't stop Ubu Roi seeming like a juvenile drag at points. But this sprawling saga about revolting financial greed and monstrous dictators has its hilarious and trenchant moments.

'Once' (0844 871 7629) to 30 Nov; 'Ubu Roi' (020-7638 4141) to 20 Apr

Critic's Choice

Katherine Parkinson’s recently widowed Laura shocks her Home Counties family in Before the Party, Rodney Ackland’s oscillating seriosatiric gem from 1949, at London’s Almeida (to 11 May). The RSC celebrates Shakespeare’s birthday in Stratford-upon-Avon with free ticketed workshops for kids, teens and adults (Sat). Try your hand at stage fighting, verse-speaking, singing, gory make-up, skull design and storytelling.