If this was a Paul Greengrass film, it would start like this. An aerial shot over central London. Digital letters flash up at the bottom of the screen saying: "LONDON, 1400 GMT". A few cellos begin stirring ominously on the soundtrack. Then a hand-held camera tracks an oblivious reporter walking through Mayfair. Somewhere, a man with an earpiece looks at a flashing dot on a screen and says, "Subject proceeding east towards Claridges." Drums start up on the soundtrack. A short clip of Greengrass himself, perhaps finishing off his lunch. The shaky camera follows the reporter into Claridges, pitching through the revolving door to chase him up the stairs. The drums get heavier. The camera dashes down corridors after him. Greengrass strolls casually towards his suite. The drumming reaches a deafening frenzy, as if a tribal sacrifice is about to take place. Earpiece man says, "He's right on top of you!" The reporter bursts into the suite. The drums suddenly stop. And . . .
Well, anyone who's seen The Bourne Ultimatum knows that Guardian journalists don't come off well in Greengrass's films. Unlike Jason Bourne himself, we tend to panic in intense situations and get a bullet in the head as a result. Greengrass is a big man, but looks light on his feet, and is dressed casually in jeans, blue V-neck jumper and black trainers – as if for action. You probably wouldn't pick a fight with him. "It was fun, though, wasn't it?" he laughs, when reminded of Bourne's Guardian cameo. "A good commercial for the Guardian, I would have thought. My love letter to my newspaper."
In truth, there is nothing remotely sinister about Greengrass. You could say he is one of the good guys, and not just because he reads the Guardian. A former World In Action director, the 55-year-old Englishman's success in Hollywood has been all the more surprising for the fact that he has hung on to his political principles. Equally remarkable is the way that trademark Greengrass style has lent itself to both rigorous factual dramas and far-fetched popcorn movies. Bloody Sunday, his stripped-down account of the 1972 Northern Ireland shootings, and United 93, his tense chronicle of the 9/11 plane hijacking, brought him acclaim and awards. His two Bourne films, on the other hand, raked in more than $700m (£465m) at the box office, and still won awards. His non-fiction works have the urgency of action thrillers while the Bourne films were shot through with real post-9/11 paranoias – waterboarding, black ops, global surveillance.
His new film Green Zone has been described, not inaccurately, as "Bourne goes to Iraq". As such, it interweaves those two discrete strands of Greengrass's work to produce a movie that is both real-world political commentary and thrilling action ride. As you would expect, the Greengrass style is in full effect: shaky camerawork, adrenalised pace; and Matt Damon charging into danger accompanied by, yes, lots of frenzied drumming. But Damon is not an amnesiac spy here, he's a good soldier searching for weapons of mass destruction in the immediate aftermath of the 2003 invasion. We all know how that's going to work out. When Damon's character realises that he is working to faulty intelligence, he sets about uncovering the truth.
"I don't really start with a story; I start with the area I want to be in," says Greengrass, explaining the movie's genesis. "It was summer 2004, and I was thinking about 9/11 on the one hand and the war in Iraq, which was less than a year old, on the other. Those twin events are what are driving our politics and our culture, and that was the headwind that was making the Bourne films lift. So I wanted to make a film about the real world that was begetting those Bourne feelings, a film that basically asks that audience to step behind that curtain."
Damon's journey in the film mirrors Greengrass's own. In real life, Damon, one of Hollywood's most vocal liberals, had been against the Iraq war from the outset, but Greengrass was not initially opposed to it. "I didn't like going to war. It was obviously deeply uncomfortable and problematic, but I remember when that big march happened [London, February 2003], I said I wasn't going on it because I'd listened to Tony Blair and, in the end, I believed him. He obviously knows stuff that we don't know, I thought. Well, how wrong was I?"
That sense of betrayal sent Greengrass on an intensive fact-finding mission. He has read all the key books and reports and interviews on Iraq – Bob Woodward, Seymour Hersh, James Risen, Thomas Ricks, and particularly Imperial Life In The Emerald City, by Washington Post correspondent Rajiv Chandrasekaran. Chandrasekaran's book meticulously details the almost comical levels of incompetence, ignorance and infighting that went on within the Green Zone, the coalition's secured Baghdad enclave. Greengrass's team optioned it, but his film is not an adaptation. The movie was written by Brian Helgeland, screenwriter of LA Confidential, among others, and despite being a work of fiction it closely follows the reality. Damon's character is based on a real-life US army WMD hunter named Richard "Monty" Gonzales, who was hired as a consultant on the film. There is a bickering CIA veteran and a neocon bureaucrat (Brendan Gleeson and Greg Kinnear, respectively). There's a secret informant named "Magellan", loosely based on the discredited "Curveball" and an Ahmed Chalabi-like Iraqi exile waiting to take the presidential reins.
Greengrass has a lot to get off his chest. He talks at length about the machinations of the US and UK intelligence structures, Blair, Alastair Campbell, the Chilcott inquiry, and so forth – so long that I start looking at my watch, wondering if I'm ever going to get another question in. He even gives me a dossier (for want of a better word) he's written, entitled How Did We Get It So Wrong?, which succinctly details the US and UK's choreography of the whole Iraq/WMD affair, with extracts, figures, bullet points and footnotes. It is galvanising stuff. It would make a good treatment for a Bloody Sunday-style docudrama, in fact. So why did Greengrass feel the need to fictionalise all this information and put it into a Hollywood blockbuster format?
"I thought at one point about doing a very small, austere film," he replies. "But then I thought, if I'm going to make a film about Iraq, I'm going to see if I can bring that Bourne audience with me. They're mostly young people – the same people who are going to go off and fight that war, and also the audience that are vehemently opposing it." We move on to talk about something else but he interrupts to re-answer the question. "Most of all – this is the core of it really – it was a film made out of my sense of affront and anger. I wanted to say, 'I know what you did.' And that statement has immeasurably more power if it's made to a broad audience in the vernacular of popular genre cinema."
Many Hollywood movies have attempted to address the Iraq war and failed – Lions For Lambs, Rendition and Redacted to name a few. The sole exception is Kathryn Bigelow's The Hurt Locker. Like Greengrass, Bigelow has a penchant for tough, action-led storytelling. But where The Hurt Locker was studiously apolitical, relatively cheaply made and spare to the point of abstract, Green Zone is brazenly political, relatively conventional in storytelling terms, and, by all estimates, pretty expensive – some put the budget as high as $150m. How will it play in the US heartlands? As an offputting dose of Hollywood liberalism, or a Bourne movie with added credibility?
Greengrass is aware that the film is a risk, but then it has never really been any other way. His career could be characterised by a willingness to wade knee-deep into situations that others would rather tiptoe around. He made a few short films as a schoolboy, mucking about with props in the art room, and really fell in love with the medium as a teenager and through university – key films being Jean-Luc Godard's new wave classic À Bout de Souffle and conspiracy thrillers such as Three Days of the Condor and All The President's Men. "The thing is, there was no British film industry at that time," he says. "It never occurred to me to try to make movies, but naturally, my imagination gravitated towards television that had the same attack and energy." That was Granada documentary series World In Action, which appealed for its "strange, eccentric and brilliant marriage of pure film-making, investigative journalism, radical politics and a non-London focus," he says.
Greengrass was told by World In Action producer David Plowright, "Don't forget, your job's to make trouble." He obliged with documentaries on Northern Ireland, the Ku Klux Klan and MI5, the latter leading him to ghost-write Peter Wright's book Spycatcher, which the Thatcher government famously tried (and failed) to ban. When he moved into feature docudramas he again tackled confrontational topics – the Falklands and Gulf wars, the Omagh bombings, the botched investigation of the murder of Stephen Lawrence. That phase of his career culminated in Bloody Sunday, which won him the Golden Bear at the Berlin Film Festival. That was when Hollywood sat up and took notice.
He admits the success of the Bourne films gave him some bargaining power but laughs at the suggestion that he is now some kind of Tinseltown power broker. "Honestly and truthfully, I don't feel I have any more power to tell the stories I want to tell today than I did when I was a young bloke on World In Action," he says.
There are no signs of transatlantic drift yet. His base is still the UK. He lives in a farmhouse in Oxfordshire with his wife and three children (he has two grown-up children from a previous marriage). He used to be a keen amateur footballer and is a lifelong Crystal Palace supporter, although he was recently spotted with Damon at a Chelsea-Arsenal match.
The Bourne films have undeniably had an impact in Hollywood. They have measurably influenced the whole tone of action cinema. It's easy to forget, for example, that when Bourne was first giving audiences visceral fist-fights and grown-up paranoia, Bond was still larking about with Madonna cameos and invisible cars. The recent Daniel Craig reboot, producing a meaner, more credible Bond, might never have happened if Bourne hadn't upped the game. They even borrowed some key members of the Bourne crew to give it that Greengrass-style immediacy. Didn't the Bond producers ever try and tap him up?
"Er . . . no," he says, with an intriguing pause. Would he do a Bond movie if asked?
"I wouldn't in actual fact, no. Anything I could say in that area I would say with Bourne. I like Bourne because it's not Bond."
So what's going on with Bourne? Universal asked Greengrass to make another Bourne film, and he agreed at least to help develop one. "I felt like I ought to because I know how important it is to them," he says. But he abruptly withdrew from the project last December. According to some reports, he was displeased to discover the studio was developing a "parallel" script behind his back. Greengrass denies this, and says he remains on good terms with the studio, but Damon has also said no to any future Bourne films, and the franchise is currently on ice. "I didn't feel the fire in the belly that you need to spend 18 months, 20 hours a day, seven days a week, to make a Bourne film. There were other films I wanted to make. And also, I felt these have been four interlinked films about the Bush years [his two Bournes, alongside United 93 and Green Zone]. I felt I didn't have anything more to say, the same way I did after Bloody Sunday. I want to say new things."
He is rumoured to be doing a film about the Vietnam war, and doesn't rule out a return to documentary and TV work, but he is keeping his mouth shut for the moment. "Funnily enough, I had a meeting last week in LA where they asked me to do a big children's movie," he teases. It's an enticing prospect: images of Harry Potter going rogue and waterboarding Voldemort spring to mind. "It's not going to happen, though," he laughs. "But it could be that kind of thing. That's what you have to do to stay ahead. It keeps you younger."
• Green Zone is in cinemas from 10 March.