Charm and the natural performances of its two young protagonists are the keynotes of Garth Jennings’s pleasing, if uneven British film.

He also made The Hitchhiker’s Guide to the Galaxy, and the eccentricity of that decent shot at the impossible is carried over here. So is his propensity to follow good comedy scenes with sequences which don’t quite work.

Some have dubbed this small-budget film, for which Warners paid $8 million shortly after its Sundance Festival premiere, the new Billy Elliot. But it hasn’t the consistency of that film, and not quite enough of the flair.

We first see naughty boy Lee (Will Poulter) sitting in a cinema where every single member of the audience seems to be smoking (this is the early Eighties, summoned up well). He’s watching Stallone’s Rambo: First Blood. It is an instant inspiration to him — and he has a video camera, too.

But school and family are a bit of a trial to Will (Bill Milner), the other central character, who is not allowed by his strict Plymouth Brethren family to go to the cinema and has to leave the classroom at school when the teacher shows a documentary.

It is outside this classroom where Will meets Lee and forms an uneasy friendship. Together the boys decide to make a First Blood of their own, with Lee as willing slave and stuntman. Their adventures along the way are what gives the film its plot.

The first sequences are splendid: after they have upset the school’s goldfish bowl, bully Lee persuades the timid Will that the head will torture them and promises to take sole blame if Will gives him his watch.

The introduction of a busload of French kids, among them a young Parisian punk (Jules Sitruk) whom everyone rather surprisingly admires, is done with wit and just a little subversive irony.

For the first half hour one thinks not of Billy Elliot, but of Ken Loach’s Kes. But the twists and turns of the story, and the making of First Blood as Son of Rambow, becomes somewhat rambling and discursive.

When one of their many mock-heroic stunts goes awry, Lee lands in hospital with a broken leg, feeling betrayed by his hitherto obedient companion. But Will’s determination to finish the movie, with Lee’s elder brother (Ed Westwick) blundering through his vital cameo role, becomes a triumph of hope over expectation.

The chief pleasure here lies in the two talented young actors, both entirely at ease in their contrasting parts. They carry Son of Rambow, with the adults trailing behind in rather onedimensional parts. In the end, you think of it as a nice rather than effortlessly flowing film.