It is hardly surprising to discover that the high-octane violence of John Woo has been censored. But Ryan Gilbey finds the director is a man who treasures emotion in his films and yearns for the human touch.

John Woo's films are ostentatious banquets of violence. You are never more than five minutes away from a shoot-out. His knack for choreographing surreal action sequences means that his characters never have to worry about the laws of physics or gravity. They fly through the air with the greatest of ease, these magnificent men with handguns in both fists and an apparently endless supply of ammunition.

When censorship finally caught up with Woo, it was not in the way he had anticipated. The censors in Hong Kong banned Young Dragons, his first feature, fearing that young audiences might imitate its scenes of violence. When he arrived in America at the start of this decade after 20 years as one of the world's most successful and influential action directors, he naturally thought that such incidents were behind him. It was a reasonable assumption, given that he was worshipped in Hollywood.

He made his American debut with the Jean-Claude Van Damme vehicle Hard Target, and no sooner had he called the final "Cut!" than the studio waded in brandishing their scissors. The violence wasn't a problem. The dramatic content was. "Originally the film was pretty emotional", says Woo, a small, excessively polite man, when I meet him at London's Dorchester Hotel.

"The first cut was stylish, too. Slow-motion, freeze-frames, lots of drama."

A specially invited audience of Jean-Claude Van Damme fans were crammed in for a test screening. Unable to cope with a film which sometimes went whole minutes without featuring Van Damme kick-boxing or displaying one of his magnificent oiled pectorals, they switched into "Do not compute" mode and responded the only way they knew how, with derision; the studio executives panicked. The dramatic scenes were excised, leaving something closer to pure action. And pure poppycock.

"The studio were afraid", Woo says, "so they removed any scene that had genuine emotions and genuine heart in it. That really hurt me."

Now Woo is having the last laugh on those who doubted that he could make the transition from cult favourite to mainstream director. His new film, Face/Off, is an ingenious thriller in which notions of identity and moral responsibility are rigorously investigated. Did I mention that lots of things get blown up, too?

It tells the hilariously implausible tale of a cop (John Travolta) and a psychopath (Nicolas Cage) who, for reasons too convoluted and absurd to venture into, swap faces and irrevocably alter each others' lives. The repercussions are infinite, and infinitely fascinating. Some cultural commentators argue that the film's success is down to Woo favouring good old-fashioned stunt work over CGI (computer generated imagery). They're wrong. Face/Off has grossed around $10m in the US because people love it when you mess with their heads. It is the best brain tease since Terminator.

John Woo turned down the screenplay six years ago, because it "was too sci-fi". Three years later, it turned up in his in-tray once again, with significant alterations.

"It was better", Woo says. "But I suggested further changes to make it more human."

Human is a word that keeps cropping up when you talk to John Woo. Is it a reflex action to divert your attention away from his films' violence and towards their consistently impeccable moral fibre?

Despite the fact that Face/Off features a body-count that is quite possibly in quadruple figures, Woo talks most enthusiastically of its humanity, its emphasis on "family values" and attributes its success to the fact that "human goodness is international."

I ask if the film is in fact motivated by the Travolta character's struggle to come to terms with the death of his son. Woo is quick to puncture my pomposity. He just smiles and says: "Yeah."

It's true that he is a conscientious director, sometimes to the point of absurdity, as demonstrated by the presence of doves in Face/Off, or the lingering shots of deer grazing and butterflies fluttering moments before a nuclear explosion in his latest film, Broken Arrow. "These things are to show that I am a very hopeful person", he says. "There is always hope. Even though the world is full of ugliness. Look at the characters in my work. They are usually somewhere between good and evil, because you will find that there are no real bad guys in humankind. We can learn from the best, but we can also learn from the worst."

I suddenly feel very humble indeed, and instantly resolve to be kind to children and estate agents for the rest of the week.

When he goes on to tell me that he counts as his hero anyone who possesses a good heart and is always kind to others, I am genuinely moved, a feeling which is only slightly diminished when I read that same line in two other interviews with Woo.

Anyway, I'm not about to doubt the sincerity of a man who can find such a succinct method of channelling his conscience into his art, as this director does in one exceptional sequence in Face/Off. The situation is a messy and violent shoot-out. So far, so Woo. But with one crucial exception: it is shot in slow-motion from the perspective of a young child who is listening to "Over the Rainbow" on a pair of headphones.

How did this daring scene come to fruition?

"The script just said: the gang are being ambushed and the hero saves the little boy", he remembers. "As we started shooting it, with people firing at each other, I thought: This is boring! I started thinking about the real world. Why do people have to kill? What is a human life worth? Can't we just stop killing and talk?

"Let's change the whole scene by putting a headset on the boy and playing music over the violence, with the song showing the innocence and purity of the child. I wanted to get that anti-violence feeling. I was so excited - it was all so spontaneous! But those are the moments which make the producers panic."