Declan Bennett & Zrinka Cvitesic
Declan Bennett & Zrinka Cvitesic
© Manuel Harlan

As in all the best original musicals, the subject matter of Once is unpromising: Dublin busker meets Czech married mother, fixes her hoover, falls in love on the rebound and makes melancholic music with her in the back room of a piano store.

But Once , faithfully adapted and embellished by playwright Enda Walsh from John Carney's modest little film, won eight Tony awards on Broadway, and its best song, "Falling Slowly," an Oscar, and is a genuine surprise, simple and affecting, and full of fresh music and a wonderful ensemble spirit.

Director John Tiffany and designer Bob Crowley have taken the film off the Dublin streets and into a big, brown, lamplit Dublin boozer, fitted out with mirrors and portraits, where Declan Bennett's Guy – much less wired, abrasive and irritating than composer Glen Hansard in the movie – and beautiful Croatian actress Zrinka Cvitesic's Girl – play out their off-kilter love story.

They are supported and surrounded by ten brilliant dancing, singing and instrument-playing actors – we have acoustic guitars, mandolins, accordion, cello, banjo and percussion – as various Dubliners, musicians, Czech immigrants (speaking English with Czech sur-titles!), family (Guy's old Dad, Girl's fable-spinning Mum) and friends.

With Tiffany's Black Watch colleague Steven Hoggett doing the movement, there is a theatrical fluency to proceedings the film lacked, but no skimping on the rawness of the songs or the sheer brilliance of the climactic ensemble rush on the recording session item, "When Your Mind's Made Up," the first big West End song composed in the hectic, disarming five-beats-in-a-bar rhythm, I reckon, since "Everything's Alright" in Jesus Christ Superstar.

The songs by Hansard and his film co-star Marketa Irglova are folk love songs without the darkness or lyrical weirdness of say, Tom Waits, but with loads of ear-grabbing intensity and heart (the word recurs throughout the show) and a spontaneous mastery of form; the impact is not dissimilar to that of Jonathan Larson in Rent, and it turns out that both shows were hatched in the same New York workshop theatre.

One risk that almost backfires badly is the over-deliberate pacing, so that the show comes down only 15 minutes shy of three hours. There's a merry ceilidh-style prologue with audience members mingling on the stage supping pints, then the Dad character (Michael O'Connor) recites a Patrick Kavanagh poem and you start to wonder if the blessed thing will ever start.

The Act Two bust-up isolating the gay Cork bank manager (beautifully done by Jez Unwin) from the Dublin boyos (a Walsh initiative) also takes far too long, and the night-time outing over the bay, ditto. But all is forgiven (well, almost) when the company dissolves into the magical a capella "Gold" and the sustained dying fall of the resolution is shaken up in a joyous reprise of the main song. There's a good gag at the expense of Ronan Keating, too.