A week after noting one five-star Scottish film, I'm heralding another - albeit of a vastly different ilk.

Whereas Filth was a pitch-black comedy, Sunshine On Leith is, as its title suggests, all light. It's the feel-good film of the year by a Royal Mile.

The title is borrowed, of course, from The Proclaimers, with Stephen Greenhorn adapting his stage musical which adeptly applied several of the duo's songs to a story of Leith romance. The comparison has already been made with Mamma Mia! Yet while the film version of that musical was as corny as it was euphoric - great songs, but a scratchy plot and some cringeworthy singing - Sunshine On Leith unites its musical quality with authenticity, making for a much more satisfying whole.

Peter Mullan and Jane Horrocks play Rab and Jean, a happily married couple preparing to celebrate their 25th weeding anniversary when their soldier son Davey (George MacKay) returns from Afghanistan with his friend Ally (Kevin Guthrie) in tow.

As Ally resumes his relationship with Davey's sister Liz (Freya Mavor), Davey starts to date Liz's nursing colleague Yvonne (Antonia Thomas). And so three relationships are on a high, until a mistake in Rab's past returns to haunt him and the youngsters contrive to lose their way.

In many ways it's a straightforward romcom set-up of love found, lost and hopefully found again; but it is given depth by the parallel romances and, of course, by the songs - the Reid brothers' lyrics adding toughness and veracity to proceedings, their melodies alternately rousing and sweet.

It opens dramatically in the Afghan desert, a group of nervous young soldiers in a personnel carrier suddenly breaking into Sky Takes The Soul, just before a bomb explodes. Having survived the blast, the two friends return to Edinburgh and civilian life. They're chalk and cheese - Davey is tall, blond, calm; Ally is short, dark, impetuous - but end up in the same routine job, manning telephones.

Davey's is a stable, happy household, which offers a model to each of them. "I wanted your mum, I wanted kids, I wanted Hibs to win the league," says Rab when asked of his youthful ambitions, "two out of three's not bad".

It's one of those musicals where song and dance evolve from the story, the most natural occasions being the anniversary ceilidh, and when the two friends happily dance in the street on their return to Edinburgh. Incidentally, there's a blink-and-you'll-miss-it appearance here by the Reids, exiting a pub.

Highlights include Mullan's gruff but believable rendition of Oh Jean in the ceilidh; Guthrie and Mavor's incredibly romantic Make My Heart Fly; MacKay and Thomas's hair-bristling duet of Then I Met You; Horrocks's gorgeous account of the title song (reminding us of her performance in Little Voice); the ensemble singing Letter From America, then - of course - I'm Gonna Be (500 Miles) as the finale.

With his first film behind the camera, Wild Bill, actor-turned-director Dexter Fletcher (a Londoner, but don't hold that against him) took the tired, British crime genre and made it fresh, funny and surprisingly engaging. He has performed the same trick here, offering all the romcom beats and a city at its glistening best, but investing this musical with genuine character and soul.