Interview: Gareth Edwards, film director - How to make a fantasy on a shoestring

• Monsters is the story of how samples from a crashed Nasa space probe thrive and grow into giant, tentacle-sporting creatures inhabiting land close to the US/Mexican border known as the "infected zone"

ANYONE paying attention to the way digital technology has shaped movies over the past decade will be familiar with the now standard refrain that it has freed up filmmakers to tell stories that would not otherwise have been possible. It's a claim slightly devalued by the fact that the filmmakers doing most of the proselytising – James Cameron, Steven Spielberg, George Lucas, Robert Zemeckis – tend to have hundreds of millions of dollars at their disposal to create their limitless fantasy worlds.

At the micro-budget end of digital filmmaking, it has been a very different story. Directors with ambitions that extend beyond dialogue-driven comedies or dramas have, for the most part, been forced to make a virtue of their budget limitations by working them into the look of the film.

That is, until now.

In the new film Monsters, British director Gareth Edwards has taken the next evolutionary step in the democratisation of the film industry.

Using off-the-shelf software, commercially available equipment, a minimal crew (never more than six or seven people at a time), and a lot of filmmaking acumen, he's made an epic-looking sci-fi film on a shoestring budget that bridges the chasm-like gap between the home-movie aesthetic of DIY ventures such as Paranormal Activity and the robust effects work and professional sheen of mid-level studio fare such as District 9.

Part road movie, part love story, part political allegory, the film – which takes place against the backdrop of an astonishingly rendered alien invasion – may not exactly qualify as a bedroom blockbuster thanks to its location shoot in Mexico, Belize, Guatemala and Texas, but it is a unique example of what's possible when you combine old-school run-and-gun guerrilla filmmaking with cutting edge digital effects. It also marks out Edwards – who wrote and directed the film, and did all the post-production effects on his laptop – as the ultimate multi-tasker.

"It's funny because I listen to the way I must sound when I talk about how small the crew was and I must come across like some kind of control freak," says Edwards, nursing a hangover in the Filmhouse bar the day after Monsters' triumphant Edinburgh International Film Festival premiere. "But it's not really that at all. It's just that film, because of its very nature, has always been an industrial process, so you've always needed lots of people just to make something. That doesn't feel like the ideal way to do something creative to me… (but] I do feel that filmmaking is breaking out of that now and into this area where individuals with very small teams can possibly compete with films that used to take hundreds or thousands of people to make."

Having already wasted a lot of time and money learning how to fill out funding applications at film school in his early 20s, it's not hard to understand why Edwards sounds so optimistic about the possibilities that now exist. After graduation, he purposefully trained himself in the art of computer animation, honing his skills doing special effects on British TV shows in preparation for the day he'd be able to make Monsters.

Not that it was plain sailing when he finally sat down to write it.

Driven by a childhood passion for monster movies, his initial plan was to make one shot on handheld camcorders on the day of an alien invasion. Cloverfield's arrival soon killed that idea, though, so he started thinking about the next logical progression and eventually found inspiration on a beach holiday abroad.

"There were basically some fishermen pulling a net out of the ocean and they were struggling with it," says Edwards, picking up the story. "I remember thinking, 'What's on the other side of that net?' And I couldn't help but imagine some strange creature with a giant tentacle.

"When I watched the fishermen, though, they were obviously just carrying on as normal, and I just thought: 'this is really interesting; maybe there's a possibility of doing a monster movie set so far down the line that nobody cares any more and life just goes on."

He thinks of a more fitting analogy. "It's like, if Godzilla was September 11th, then this is like the War on Terror five years down the line, when everyone has lost interest and it's just on TV and only seems to affect certain people directly."

Inspired by scientific reports about the possibility of life on one of Jupiter's moons, Edwards developed a back-story for Monsters involving a Nasa space probe crash-landing in Mexico on its return from collecting samples. The film takes place six years later, when said samples have thrived and grown into giant, bioluminescent, tentacle-sporting creatures inhabiting a strip of land close to the US/Mexican border known as the "infected zone."

With the local inhabitants more concerned about American airstrikes against these monsters than the monsters themselves, the film follows an opportunistic photojournalist (Scoot McNairy) who has been reluctantly seconded to guide his boss's daughter (Whitney Able) back to the US border.

It's a clever concept, not least because it enabled Edwards to keep the budget down without compromising the look of the film. "Part of what we're really talking about with this guerrilla approach to digital effects filmmaking is not being regimented by a specific vision. It's more a case of: 'I'm going to turn up, see what happens and what environments we've got and incorporate them into my story.'"

He's not kidding. Knowing he'd need apocalyptic scenes of devastation, he kept his eye on the hurricane season in the US and got permission from local authorities to shoot some of the film in Texas in the aftermath of Hurricane Ike, making a donation to the clean-up operation and transforming his own uneasiness about the ethics of shooting in a disaster zone into a subplot in the film. An improvised scene shot during the Day of the Dead festival was also turned into a texture-creating plot point in the final edit.

It hardly needs to be said that such an approach made a script unfeasible. Instead Edwards wrote a detailed treatment with the characters' physical and emotional journeys locked down, and relied upon real-life couple McNairy and Able to improvise much of the dialogue and respond to their surroundings. This did lead to a surreal moment after the movie was finished when Edwards took delivery of an actual script after someone had transcribed the finished film for subtitling. "We actually thought about sending it out to a few studios and asking them how much they thought it might cost. But the reality is that it would have cost a fortune because what's on the page would be dictating what everything had to be."

The big question now is what effect – if any – Monsters' successful use of digital technology will have on blockbuster filmmaking. "That's what's going to be so interesting," says Edwards. "Are there X number of good films per year because there are only X number of good filmmakers? Or are there only X number of good films because only so many films can be made each year? It's really hard to know, but I do think things are going to change a lot in the next ten years."

• Monsters is released on 3 December