Paul Greengrass has become one of the hottest filmmakers in Hollywood in a relatively short space of time and is renowned for his no-nonsense, hand-held shooting style. A lot of his work deals with contemporary issues, such as Bloody Sunday, which looked at an infamous chapter in Northern Ireland's recent history, and United 93, which offered a real-time account of the events on board United Flight 93 on September 11, 2001. Even his Bourne movies - Supremacy and Ultimatum - exist in a contemporary world that never seems to far from the headlines. He tells BBC Movies why he's drawn to those kinds of movies and why the Bourne films represent such a special franchise...

What drew you back to the Bourne franchise for a second time?

Well, because I love the franchise, I love the character and I love the world. I think if you're making films in Hollywood the franchise bit of the business is very, very important because it's the gigantic engine that drives it all. If the franchise films aren't working then we don't get to do the other films that we want to make. So, when you look at the huge engine room where these big, big movies get made, most of them tend to be superhero movies, or movies about characters with magical powers. They tend to be the province of fantasy or comic book-based characters. I love two things about the Bourne franchise...

Firstly, I think that from top to bottom, every single one of us tries their best to make an original, interesting film. That may sound like a bit of an obvious thing to say but it's very, very easy in the mainstream to have the edges knocked off and end up with something that's a bit bland and a little bit safe. It's the thing about the franchise that I'm most proud of and it's what brought me back. Secondly, the character is not a fantasy character; he's a real man in a strong contemporary landscape. He's a character with depth, and the world is urgent - the storylines feel like they could be ripped out of tomorrow's newspapers. When you take that as a package - that desire to create really good, original contemporary work in the mainstream - that's what brings me back.

How difficult was the scene at Waterloo from a technical point of view?

Directing a Bourne film is chaos like you've never ever seen, believe me! But the reason for that is the Bourne films are a very interesting collision between a sort of indie mentality, which is where [original director] Doug [Liman] would come from, and the mainstream Hollywood mentality. The problem when you come to make the third film is that by the end of Supremacy, it's clearly a very, very successful commercial franchise, so the Hollywood bit of it is very well entrenched. So, coming into the third one it was all about how do you get the indie thing to live?

Well, one of the ways you do it is to try your luck and set the action in places where you can't behave like a big movie... because there's a temptation when you have a big movie to put up the picket fence, put the trucks inside, build the sets and operate in a very efficient manner. But if you set the action sequences in places like Waterloo or Tangier or even on the streets of New York, you can't behave like a big movie; you're forced to be like a student filmmaker and make it up as you go along, live on the land and shoot when people are around. But I think that shows. I think it gave us a kind of vitality.

Is the technology used by the CIA in the film actually possible?

Well, the Echelon thing is real, the key word tracking. I don't actually think they can track it quite as quickly as we make out but it's certainly possible. I also remember thinking when we did the sequence at Waterloo how excellent it would be if they could tap into the camera network. But we said they couldn't do that because it would be preposterous - and then we checked and realised that they could.

Was there ever talk of an alternative ending for this latest Bourne film, to keep your options open?

I would never support ending the character's life because to me Bourne is all about certain values. What I like about the franchise is that Bourne is not about wearing Prada suits and looking at women coming out of the sea with bikinis on. This film really is about finding answers and more time was spent on trying to find the right kinds of answers.

The interesting thing about a Bourne film is that you very often find that because they're ultimately so simple, they're also fiendishly difficult when you make them to arrive at that simplicity. I've made two of them and very often you're circling endlessly around a very small number of scenes that you shoot sometimes in four or five different ways. Matt [Damon] and Joan [Allen] had a scene that I think we shot four or five different times. You're endlessly re-shooting scenes because you want the piece of the jigsaw - and you know you want that piece but it's finding the exact way to do it rather than shooting lots of different scenes and lots of different stories.

Matt Damon has said that if you signed up for a fourth Bourne movie, there would be a case for him doing it as well. So, will there be a fourth Bourne movie?

Um, well it's not something I've actually given any thought to. The thing that's lovely about the Bourne franchise is that so far no decisions have been made cynically or commercially. I remember at the end of Supremacy you could just feel people coming out of the theatres wanting another one. And they're the people who should decide that - not me or the studio or anybody else. If the audience wants another one, that'll be because there are some unresolved questions. They won't want one if they feel that the story has come to its end. As far as I'm concerned I'm going off and doing another movie so I'm not going to be thinking about Bourne for a couple of years... if ever!

Will you continue working on the themes of fear and paranoia in a post-9/11 world?

I don't know. I don't think you ever set out to make a film in that genre and if you do you wait until it's distilled in your mind. Maybe. You swim in the tide of the world you live in and obviously the films I tend to make are contemporary, so that's going to dictate how those films are.

The Bourne Ultimatum opens in UK cinemas on Thursday, 16th August 2007.