If you were lucky enough to see the trailer you may have thought that Sunshine on Leith was a spoof. A musical featuring a couple of singing squaddies, set in Edinburgh, featuring the songs of the Proclaimers? And what’s this…directed by no less a maestro than Dexter Fletcher?! What set of circumstances, you’re entitled to ask, allowed such a thing to happen and can it really be as bad as it sounds? Well despite a marketing effort that bent over backwards to convince us it was a setup, Leith is a real movie, and one based on an extant stage play by Stephen Greenhorn. Someone, somewhere thought this provincial offering would play well nationwide but the result’s a better argument for Scottish Independence than anything that bigoted ol’ separatist Alex Salmond’s come up with.

There’s no question that if you’re in the mood, a sort of twee high, then you’re going to be beguiled by this unashamedly good natured and un-cynical piece that invites you to spend 100 minutes in a romantically affected Scotland where you can’t enjoy a dram without the house breaking into song, and where hidden amongst Joe and Jacinda Public are flashmobs of theatre school students, ready to segue into a half-choreographed dance routine at the drop of some skag. That the story plays out in an alternate reality can’t be in doubt, because if these saccharine, dimple stretching numbers were suddenly unleashed into real Scottish pubs, there’d be carnage, with the instigators handed their jawbones on the way out.

Any musical lives and dies on the strength of its songs. Sunshine on Leith cobbles together some old tunes from The Proclaimers album of the same name, plus one either side, and whereas the hits remain thus – the likes of Letter from America and I’m Gonna Be (500 Miles), the rest are toe-curlingly saccharine, not to mention oddly truncated. More than a few numbers last just a verse; as though Fletcher was reluctant to let his film morph into a full blown musical extravaganza. But as any genre aficionado will tell you, there can be no half measures when it comes to a sing-along spectacular. Patrons expect a show, and here too Fletcher errs; his staging of the numbers lacking vitality and, most egregiously, notable choreography.

Unwilling or unable to spend the extra £200 a day on a dance teacher, Fletcher’s direction to most of his background cast seems to have been “wave your arms”. Yes, there’s plenty of waving, oodles of swaying but little in the way of those moments when ordinary environs are magically transformed into performance spaces, awash with carefully coordinated movement and the creative use of props. Ultimately this marriage of insipid tunes and uninspired direction causes the whole caboodle to fall flat. Even the worst American musicals, the likes of Grease 2, tried harder than this.

Shorn of the musical interludes, there remains a well-acted and likable melodrama, in which new faces like Antonia Thomas, batting away some ugly anti-English sentiment, hold their own against cast iron reliables like the crag-faced Peter Mullen and Jane Horrocks. What’s lacking is the magic that accompanies the best film musicals – that sense of being transported to another place, where no one bats an eyelid at any leading phrase instigating a full blown song and dance routine. Fletcher gets good performances from a game cast but I wouldn’t give you half a sixpence for his skills as a musical impresario.