Joel and Ethan Coen: The brothers grim

It's 10.30am, the morning after Joel and Ethan Coen's latest film, Burn After Reading, has opened the Venice Film Festival. Carrying huge cups of coffee, the sibling film-makers troop into the appointed hotel room looking like bespectacled hippie academics having bad-hair days. At 53, Joel is the older by three years, and everything about him suggests he is the more senior: he's more sombre than his younger brother, and his beard has more flecks of grey in it; Joel is also taller, with a face more equine and less boyish than Ethan's.

Ethan is dressed in a white shirt and jeans and Joel is wearing much the same, a casual look that belies their terse manner with the press. Cracking open the Coens is a difficult task at the best of times. And this has been a remarkable year for the brothers, who collected Oscars for Best Picture, Director and Adapted Screenplay for their take on Cormac McCarthy's novel No Country for Old Men. A thriller that was violent even by their standards, it also became the most successful film of their 25-year career, taking $160m worldwide. "I think we're surprised if anything of ours hits," grunts Joel, when I ask if this took them aback. "It's good when it works out well," nods Ethan. "It just gives you more freedom and a little credit in the bank in terms of what you're going to do in the future."

The last time the brothers had a bona fide box-office hit on their hands was 1996's kidnap drama Fargo, which won them a Best Original Screenplay Oscar. It also won Best Actress for Joel's wife Frances McDormand (they have been together since meeting at the auditions for the Coens' 1984 debut, Blood Simple). Until Fargo, the Coens' series of idiosyncratic, genre-twisting films had been admired but never embraced. They were Hollywood outsiders, regarded with slight suspicion – a feeling that seemed to be mutual, judging by their 1991 Cannes Palme d'Or winner Barton Fink, the story of a playwright struggling in the film-studio system.

Unlike that film's eponymous left-wing hero, the Coens didn't sell their souls to Hollywood after Fargo: their next three films were the cult hit The Big Lebowski, the quirky O Brother, Where Art Thou? and the defiantly non-commercial noir The Man Who Wasn't There. That said, they came mighty close with their ill-advised 2004 remake of Ealing comedy The Ladykillers. Following on from 2003's marital comedy Intolerable Cruelty, critics were beginning to claim the Coens were washed-up. "You can't go through life worrying what people think," argues Joel. "If you're around for more than a month or two, you've got to get used to the fact that there are ups and downs. If you start letting it affect you, you'll drive yourself nuts."

Yet with No Country for Old Men, the Coens are now Hollywood's hottest directors. Burn After Reading opened in the US last month, accumulating $45m inside two weeks. (Fargo took just over half that in its entire run.) Obviously it didn't hurt having their most star-studded cast yet, led by George Clooney and, for the first time in a Coen brothers film, Brad Pitt.

Whether it's luck is open to debate – the Coens run a tight ship. Sharing writing, producing and directing duties, they also edit together under the pseudonym Roderick Jaynes. They've used the same composer, Carter Burwell, on all but one of their 13 films and costume designer, Mary Zophres, since Fargo. Yet is it a surprise that they've maintained such strict levels of control in a system that likes to extinguish individuality? "It is and it isn't," says Ethan. "Our movies are pretty inexpensive and they always do well enough so that it makes sense [to financiers]."

No doubt it helps that the Coens have an uncanny knack of attracting A-list stars willing to cut their fees. In the case of Burn After Reading, the film, a nihilistic espionage farce, is the sort of dialogue-driven piece actors salivate over: alongside regulars such as George Clooney and McDormand are newcomers Pitt, John Malkovich and Tilda Swinton. A story awash with the debris of modern life, from cosmetic surgery to sex toys and internet dating, it begins as Pitt and McDormand's gym instructors come into possession of a disc belonging to Malkovich's disgruntled CIA operative. He thinks it contains his recently penned memoir, while they believe it's full of state secrets; either way, they're all wrong. "The conscious impetus behind the plot," says Joel, "was, 'Let's make a spy movie where the information that's at stake is worthless.' The fact that it's worthless is... well, that's the mistake in perception on the part of most of the people involved. They don't realise that it's rubbish." '

It's not the first time they've depicted "a league of morons", as Malkovich's character calls them: what Ethan calls "knuckleheads" and Joel "numbnuts" often populate their work. In this case, it's a toss-up between Pitt's gym bunny and Clooney's paranoid treasury official as to who is the more inept. Still, it's tempting to think that the film's title is a sly reference to any critical assessments of the Coens' work. Certainly, interviewing the brothers can be a frustrating process – they brush off any attempts to prompt them towards analysis of their work. At one point, I venture that The Big Lebowski, with its references to George Bush Snr and the first Gulf War, is probably their most political film to date. "We didn't think about it that way," says Ethan, "but OK."

Perhaps Ethan prefers to believe that the film reflected Raymond Chandler rather more than the first Bush administration. Indeed, since Blood Simple (which borrowed from James M Cain's novel The Postman Always Ring Twice), the Coens have shown themselves unafraid to plunder literature and film before placing it all in a postmodern blender.

A forthcoming two-month BFI season highlights this, screening each Coen film alongside a direct cinematic influence (see box, right). Whether it's the high culture of Homer inspiring O Brother... or the lowbrow impact of Looney Tunes cartoons on their 1987 film Raising Arizona, much of the fun of watching the Coens' work is playing spot the reference.

So what has been given the treatment in Burn After Reading? Action movies, specifically those produced by Jerry Bruckheimer and directed by Tony Scott (notably Enemy of the State). "If we were setting up the scene," reports Ethan, "the question was always, 'What would Tony do?'" From the opening shot, they smartly mimic Scott's testosterone style. And if you think this is an example of their snickering superiority, both point out their love of Hollywood fluff – in particular the Doris Day movies they watched growing up.

Raised in a suburb of Minneapolis, the brothers come from an academic background. Their father, Edward, was an economics professor and their mother, Rena, an art-history lecturer. Joel began making Super 8 movies when he was eight, and would study film at New York University. Ethan read philosophy at Princeton "for fun", but was reunited with his sibling when he moved to New York, and got a job at a department store – an experience that found its way into their 1994 comedy The Hudsucker Proxy.

They are based in New York, but contrary to popular belief their symbiosis does not extend to them living next door to each other. While Joel lives with McDormand and their adopted son Pedro, Ethan resides with editor Tricia Cooke, his wife since 1993. Whether their domestic situations have ever influenced their work is impossible to say, for the Coens stringently avoid the autobiographical. Until now. Currently shooting A Serious Man, their first film set in their home state of Minnesota since Fargo, it might be about the closest we may ever get to seeing the Coens laid bare. "It's about a Jewish family in the Midwest in 1967," explains Joel. "It's hard to describe. Not much happens. There are a few laughs. I don't know." Talk about lowering expectations.

Its cast of unknowns is the very antithesis to the high-profile Burn After Reading, yet it's typical of the brothers to burst the hype bubble that's been building around them. Any time they come close to a mainstream career, they veer off down an unexpected path.

So how is it they retain this mystique around their work? Ethan recalls working with Billy Bob Thornton on The Man Who Wasn't There, just before he went off to make Envy with Barry Levinson. "We told Billy Bob not to tell Barry Levinson any of our secret shit. And Billy said, 'But you don't have any secret shit!' And we said, 'Yeah, but don't tell Barry Levinson that.' Maybe that answers your question." It does. Sort of.

'Burn After Reading' opens on Friday. 'O Brothers! – The Coens in Context' runs from 1 November to the end of the year at BFI, Southbank, London SE1, www.bfi.org.uk

Brotherly love: Five films that left their mark on the Coens

1. Sullivan's Travels (1941)

Preston Sturges's story of a director desperate to make a movie called O Brother, Where Art Thou? inspired the Coens' musical

2. The Long Goodbye (1973)

Robert Altman's slant on Raymond Chandler, as filtered through 1970s LA, is the template for the Coens' The Big Lebowski

3. In Cold Blood (1967)The brothers' Oscar-winning kidnap drama Fargo leans heavily on Richard Brooks' Truman Capote adaptation

4. The Glass Key (1942)

For their mob saga Miller's Crossing, the Coens swiped from Dashiell Hammett's 1931 novel and its film adaptation

5. Mr Deeds Goes To Town (1936)

The Coens' The Hudsucker Proxy drew from two Frank Capra films – Meet John Doe and this tale of a bumpkin and a fast-talking reporter JM