‘Would you like a slice of sponge cake with your cup of tea?’ Garth Jennings says amiably. ‘I made it this morning. Not sure if it’s any good, mind.’

A warm welcome aboard his floating studio, housed on a barge on a canal in north London, this may be. But it’s not quite the reception one might have expected from the 30-something Englishman who’s one half of Hammer & Tongs, the cocksure and cutting edge music video and, more recently, filmmaking outfit that’s worked with Blur, Pulp, Badly Drawn Boy and Fatboy Slim. One might have expected a more polished and professional reception, shall we say, from the creative force who helmed, in collaboration with his business partner Nick Goldsmith, the $60 million blockbuster big screen adaptation of The Hitchhiker’s Guide to the Galaxy. It turns out, however, that Jennings’ down-to-earth, hands-on and in-house welcome is fully inkeeping with both Hammer & Tongs’ working ethos and the spirit in which their latest creative venture, the marvellous retro comedy Son of Rambow, was envisaged and executed.

Son of Rambow is about a pair of scruffy ten-year-old boys living in suburban England in the early 1980s who team up to make their own version of their favourite film, Rambo: First Blood. Initially, the boys – loner Will and bully Carter – shoot their mis-titled film alone, using a video camera nicked from Carter’s wheeler-dealer brother and playing the parts of the superhuman Vietnam veteran and his fatherly former commander themselves. Soon, however, the enterprising adolescent auteurs co-opt the services of their school’s riotous sixth-formers, an ultra-cool, Gauloises-smoking French exchange student, and a daft old codger from an old people’s home played by octogenarian comedian Eric Sykes.

Aside from the pricelessly funny, amateurish but ambitious remake of the iconic 1982 action movie, Son of Rambow also recreates the experience of being a kid in Thatcher’s Britain to hilarious and, it must be said, extremely knowing effect. The film, which was the well-received List Surprise Movie at the Glasgow Film Festival last month, went down a storm at the Sundance Film Festival last year, winning Jennings and Goldsmith the coveted Audience Award. For a very modestly budgeted little British film, Son of Rambow has done very well indeed for itself. And it all started with an eleven-year-old boy from Essex named Garth running around his local woods with a camcorder.

‘We lived near Epping Forest,’ Jennings says over tea and cake in the bowels of the barge, ‘and we spent all our spare time in the forest running around and setting fire to things and watching them burn. Someone’s brother got hold of a pirate video copy of First Blood, and suddenly we’re watching this bloke running around a forest with just a knife, sewing his own arm up and chiselling the most amazing traps. We thought, “Wouldn’t it be great to do our own Rambo?!” So we made this film called Aaron Part 1. It was all shot in one day, done by teatime. It was very elaborate, and I’ve still got it here in the studio somewhere. But I won’t show it to you,’ Jennings says teasingly, ‘because it’s hideous. I might put it on the DVD of Son of Rambow, though.’

Twenty-five years or so later, Jennings has taken another bash at remaking Rambo. And even though he and Goldsmith were working with a proper budget and a professional cast and crew, the experience was, according to the writer-director, ‘as close to making films as 11-year-olds as we’ve ever been.’

Son of Rambow was shot over three weeks in and around leafy, suburban Berkhamsted in Hertfordshire, without recourse to on location video playback and comfy trailer facilities. Newcomers Bill Milner and Will Pouter (both excellent as, respectively, Will and Carter) were thrown into the deep end (and at one point into an enormous pool of fake oil) by Jennings and Goldsmith, who themselves coached the boys’ acting. The special effects – of which there are quite a lot, including the catapulting through trees of red bandana-clad pre-teen warriors – were completed in-house, or rather on a second barge next door to the Hammer & Tongs studio. (‘We just brought in a load of mates who were good at CG,’ Jennings says, ‘and they sat on the barge there and did everything.’) And finally, the film was edited together in a post-production suite adjacent to Jennings’ toy model-strewn desk by Hammer & Tongs’ staffer Dominic Leung.

‘We made Son of Rambow in a boutique-y way,’ says Jennings. ‘I loved making a big film like Hitchhiker’s Guide to the Galaxy, but the trouble with going bigger is more gets deferred. Things get taken away from you. You’re never doing it for yourself. The limitations, financial and practical, we were working with on Son of Rambow certainly inspired a bit more creativity. You can’t beat a bit of simple inventiveness,’ Jennings finishes, taking a mouthful of homemade cake.

This is the essence of Hammer & Tongs. It’s how and why Jennings and Goldsmith put Jarvis Cocker in a stair-lift, Joan Collins in a bathtub and Supergrass in puppet outfits. Formed in 1996 by a handful of London art school graduates, the original big little idea for Hammer & Tongs was to make music videos for MTV in an independent creative environment with no corporate interference. Two hundred videos and a raft of awards later, Jennings, Goldsmith and their gang are continuing to do just that.

Recently returned from some much-needed time off surfing down in Cornwall, Goldsmith picks up the Hammer & Tongs story. ‘After we graduated, myself, Garth and Dominic decided to become a directing trio. We came up with the name Hammer & Tongs, which means to go at it with all your might, and gradually we fell into the directing, producing and editing roles. Since then Garth and myself have worked closely together on everything we’ve made, from the script onwards. You’ve seen the boat. We sit back-to-back. We always know what the other one is doing. And we remain very hands-on. So,’ Goldsmith says with a smile, ‘my favourite day of the Son of Rambow shoot was when I was the safety diver in the lake scene, because I was getting my hands dirty. That’s what making a film is all about.’

Goldsmith says the transition from making music videos to making films was a pretty smooth one, largely because he and Jennings found the process of making videos and making films to be not all that different. ‘Making music videos was a great training ground for filmmaking,’ Goldsmith says, ‘because in terms of the actual shoot, setting up the cameras, directing performances etc, a film is just a very long music video. So going into Hitchhiker’s Guide we were pleasantly surprised to find we actually knew what we were doing, despite people trying to tell us how we could and couldn’t do things. Then, when we went into Son of Rambow we decided we really could do what we wanted just the way we wanted.’

The Hammer & Tongs way of working has paid off. The response to Son of Rambow has been ecstatic on both sides of the Atlantic and among the cinema-going public and critics alike. And, as Jennings informs me with evident delight, John Rambo himself, Sylvester Stallone, has seen the film and is happily endorsing it. ‘He thought it was great,’ Jennings says. ‘But then it was never supposed to be a stitch-up. I think the first film’s pretty bloody good. It was only later with the sequels that Rambo got a bit more silly and over the top and lost its way a bit. But the first one had such a big effect on me and Nick. It’s why we wrote the film, really. So having Sly Stallone’s blessing is just fantastic.’

‘I was really proud when we watched the finished film,’ Goldsmith says, ‘because it came out so close to what we wanted. Anything after that is a bonus. The fact that it did so well at Sundance is a bit surreal. The idea that you can make a film and be part of history, like ET, which will always be around, is amazing. It may not be the case with Son of Rambow, but the idea of leaving some sort of legacy is, for me, something that’s very exciting about making films.’

Son of Rambow is out on Fri 4 Apr.