Nativity Rocks! is a kid-friendly cornucopia of sentimental nonsense.

Opening with a somewhat harrowing sequence showing the arrival and separation of a father and son pair of illegal immigrants – unhinted at by the happy-clappy trailers – “Nativity Rocks!” quickly settles down into the twee, ramshackle charm of a school nativity play given big-screen licence we’ve come to expect from the franchise.

While the staff and students from St Bernadette’s Primary School in Coventry audition for a place in a rock musical competition, a young Syrian refugee called Doru is searching for his father, who he lost contact with as he entered the country. Can the new Mr Poppy (Simon Lipkin), the old Mr Poppy’s long-lost brother, reunite Doru with his family, teach a rich family the true meaning of Christmas and help the town of Coventry win the Rock Opera competition?

Of course he can. You’re not watching a “Nativity!” film because you’re expecting a “Black Mirror” style sting in the tale or anything approaching gritty social commentary. Nope, you’re looking for an hour and a half of heartwarming, lightweight buffoonery featuring a revolving door of who’s who of British thespian talent. Carrying over from “Nativity 3: Dude Where’s My Donkey?”, Celia Imrie returns as Mrs Keen, the primary school headteacher who’s content to employ a homeless, emotionally volatile, dog stealing stranger as a classroom assistant on the basis of the patches on his denim jacket, never mind anything so prosaic as a CBA check. This new Mr Poppy initially grates as he frenetically tries to out-Poppy Marc Wootton but eventually settles down a little as the movie trundles along.

What scenery this threadbare performance can afford is devoured by Craig Revell-Horwood as the nominal ‘villain’ of the piece, and while the cast’s performances vary from pleasant to panto to pine (Ruth Jones outshines the lot, bringing unexpected depth and pathos to her small but pivotal role), the children are much less archly stage-school than previous instalments and it develops its own sort of daft charm.

It’s got an unsubtle and simplistic morality to it and a ‘just because’ approach to storytelling that avoids any remote semblance of the real world implications of the antics on screen. There’s a guileless innocence to all the characterisation and all the problems, no matter how insurmountable they may seem are resolved simply and with zero consequences. Once you stop trying to judge it as a feature film, though and view it as a wish-fulfilment CBBC-style children’s comic fantasy show, it actually succeeds on its own terms, and those terms are base sentimentality and idealism delivered with ruthless sweetness and efficacy – unless I saw the film in a very dusty cinema indeed.

It may not rock as hard as it wants to, but it all rolls up into a sweet and gently topical Christmas fable that works as an over-ambitious school Nativity play.