Son of Rambow (12A)

This wonderfully sweet coming-of-age comedy opens with a shot of breathtaking sinfulness.

A boy is slumped in a cinema seat watching Sly Stallone in First Blood. In one small paw is a cigarette, in the other a video camera. So we have, ladies and gentlemen of the jury, underage smoking, bootlegging and outrageous screen violence.

Worse, the little blighter is clearly enjoying himself. It's enough to blow the gaskets of copyright lawyers and self-appointed moral guardians everywhere.

Among everyone else it will prompt a great big dirty smile. Son of Rambow shamelessly transports viewers back to what was, for some of us anyway, the good old days of the early eighties.

Others, having watched it, will leave the cinema trying to recall the last time a film made them feel so cheery. Heaven knows, it doesn't happen often. Given the unrelenting misery on offer at the average cinema these days - and that's just the Eddie Murphy comedies - I sometimes think the Samaritans should set up shop next to the popcorn machine.

Writer-director Garth Jennings and his young cast are having none of that. As the astute will have concluded, puffing film pirate Lee (Will Poulter) is a bit of a cheeky monkey. The long-suffering teachers at his London school prefer the moniker "devil child".

To quiet, shy Will, another boy in his year, Lee is an "outsider". Will (Bill Milner) is a member of the Plymouth Brethren, a religious movement that forbids watching television and going to the cinema. Whenever a video is shown in class, Will decamps to the corridor. It's there he meets Lee, who has been exiled for quite another reason.

Will is coerced into taking part in a movie Lee is making for Screen Test's young filmmaker of the year competition. (For the uninitiated, the children's quiz show was a kind of University Challenge for budding Barry Normans and Spielbergs).

So begins a long, hot summer of dangerous exploits and growing friendship, punctuated by intense drama as Will's family find out what's going on, and hilarity as a party of French schoolchildren arrive on an exchange visit.

Jennings based the story on his own childhood. In his case, making home videos of Rambo and Raiders of the Lost Ark led eventually to directing 2005's The Hitchhiker's Guide to the Galaxy. Son of Rambow finds him rediscovering that childlike enthusiasm for movies and combining it with solid comedy craftsmanship.

There's plenty of honest to goodness daftness here, but it's underpinned with deft characterisation and a strong plot. When British comedies get these ducks in a row – Four Weddings, Gregory's Girl, Withnail and I, The Full Monty, the Ealing greats and so on – the result can be outstanding. When they don't, well, let's say no more than Sex Lives of the Potato Men. Feel free to shudder.

Jennings takes care to explain why Will and Lee are so devoted to making their little film a success. Each boy is missing a father in his life. Will has an adoring mum (a lovely performance by Jessica Hynes), but she's being swayed by a creepy, overbearing suitor (Neil Dudgeon), all zipped-up anorak and buttoned-down emotions. Lee's parents have gone abroad, leaving him in the care of a bullying older brother.

Pretending to be the son of Rambow, as Will spells it, is a comfort to these lads as well as a laugh. It's rather old-fashioned, not to say downright politically incorrect, for a British film to lay such stress on the importance of dads. Nor, risking the wrath of health and safety, is Jennings afraid to let boys be boys. Will and Lee get into such jaw-dropping scrapes I kept expecting a legal disclaimer to be flashed on screen warning children not to try this at home.

Milner and Poulter are an engaging pair, both utterly lost in the moment, as only children, and the better variety of child actor, can be. At the other end of the age spectrum is Eric Sykes, playing a care home resident. The 84-year-old might only be on screen for a little while, but he nabs some of the biggest laughs.

If Jennings goes overboard on the nostalgia, using it like sticky-back plastic to bind his film together during its weaker moments, he has enough goodwill in the bank to get away with it. Like Gondry's Be Kind Rewind, his film recalls what it was like to fall in love with movies. Young Will, watching First Blood for the first time, is like Baloo the bear – gone man, solid gawn.

Watch Son of Rambow and you will be too – back to the days of endless summers, when global warming was nowt but a glimmer in a polar bear's eye, back to an age when films assigned themselves the simple task of cheering us up. It's a difficult job, but son of a gun, Jennings has managed it.

It has taken a long time for this film to arrive in UK cinemas; it made its debut in the Sundance Film Festival of January 2007 and since then it has earned a steadily growing reputation.

Perhaps because of the unrelenting torrent of praise, I find the film a little underwhelming now that it finally reaches UK cinemas. It may be a generational thing, because although the film has certain charms, I can’t get too worked up about it.

Set in 1982, Son of Rambow is essentially a semi-autobiographical tale from director Garth Jennings, who spent his childhood making amateur movies.

It’s the story of two boys: wild Lee Carter spends his time making pirate videos of mainstream hits like First Blood, while Will Proudfoot lives a closeted existence as a member of the Plymouth Brethren and is forbidden access to the modern world.

The two meet by chance; Will sees Lee’s pirate version of First Blood and his first encounter with Rambo changes both their lives.

Lee is determined to make a film to win the Screen Test young moviemaker competition and Will decides to help out by becoming the Son of Rambow.

Their relationship is tested by the arrival of a group of French exchange students, but it all works out in the end in a film that doesn’t have an edgy bone in its body.

Both boys have father issues and the film makes much of that but in the end neither storyline is especially well resolved and the ending is unreasonably sentimental.

Son of Rambow reminded me of the wholesome Children’s Film Foundation movies that used to infest cinema and television in the seventies, especially on Screen Test. That may well be a deliberate nod by the director, but it makes for a very flat film.

Jennings does insert some Michel Gondry-like animation sequences, but these only serve to highlight the visual dullness of the rest of the film.

The actual home movie provides a lot of the charm, and the two young leads – Bill Milner as Will and Will Poulter as Lee – are very engaging, but on the whole I was underwhelmed.

My guess is if you were ten in 1982 you’ll love this. I wasn’t, so I don’t.