The film centres on the relationship between a bodyguard and his young charge

The actor plays Creasy, a former Marine hired to protect a family in Mexico City. The film builds up the relationship between Creasy and Pita, played by Dakota Fanning - a young girl he is hired to protect.

Washington said that he himself had brought a strongly religious aspect into the film, having read a chapter in the Bible about men whose job it was to protect people who cannot protect themselves.

"I thought that was interesting, because what happens to them - policemen, or young men and women in Iraq right now - they're there and doing a job, and however you feel about it, what about the horrors that they've seen?" Washington told BBC World Service's The Ticket programme.

"What happens to them? Does it lead to alcohol, and abuse, like it does with this character?"

Ready to kill

Man On Fire was released in the US in April, but despite being directed by British film-maker Tony Scott, it is only being released in the UK in October.

The film is a remake of a 1987 movie that starred Scott Glen and Joe Pesci.

After an unspeakable act is carried out on Pita, Creasy seeks vengeance - Washington described him as going on the "rampage".

Pick your quote - 'an eye for an eye' or 'thou shalt not kill' Denzel Washington

But he said that the violent latter half of the film was justified by the careful build-up.

"Unusually in these type of films, you step on the hero's toe and he starts shooting," Washington said.

"We don't know his or her back-story. One of the things that appealed to me was the back-story, and what he had to go through."

He said he that his character has "one hand on the Bible and one hand on the Bourbon bottle".

Extreme retribution

Washington refuted criticism of the extreme retribution that his character deals, with a number of violent deaths.

"It's no different than war. Do you not kill because you are a Christian, or you believe in God?" he said.

"Pick your quote - 'an eye for an eye' or 'thou shalt not kill'. If you go out there, you'd better be ready to kill, because you'll get killed if you don't."

He argued further that Creasy is very much a hero - although saying more would give away too much of the film.

"I think that anybody who is willing to make the sacrifice that he makes at the end of the film is definitely a hero," he said.

"Would you do it? Would I? I don't know. In fact I think it's one of the most heroic characters I've played."

'I know what I'm doing'

And he argued that, while the film was "not a documentary, just a movie", it did pose an interesting question.

"It also suggests, what would you do?

"What would you do if it was your child? Or at least, what would you want to do?"

Man On Fire is directed by Tony Scott

The film is perhaps a surprising collaboration, given the contrast between Tony Scott's flashy, visceral directing style and Washington's often understated style - even in the thriller The Bone Collector, Washington's character spent most of the film lying in bed.

Directors have remarked that he is from the "less is more" school of acting, while one actor once commented it was difficult to see what Washington is doing when working with him - until it is seen on the big screen.

But Washington said that while he agreed he had a minimal style, it did not mean it lessens the impact of his acting.

"I think part of that is that directors don't watch the acting anymore - they watch the video screen," he said.

"It used to be that the camera was right there, and the director was next to it watching you, so that he or she could see the performance.

"No you're 45 feet away, watching some little box, and you think you need more because you can't see - and I'm like, 'Well, when it's a 50-foot screen, take a look and let me know.'