Brad Pitt - The hitman

“I apologise,” says Brad Pitt. “I'm bad at this today, aren't I?” Brad Pitt, movie star extraordinaire, 48-year-old father of six, and the world's most famous bridegroom-to-be, is sorry. Sorry that he and Andrew Dominik, the director of their latest project, Killing Them Softly, went out and hit the town the night before press interviews for the movie. Pitt sits, immaculate in a three-piece suit the colour of cream cappuccino, nursing a coffee of the same colour and – presumably – a hangover.

Fortunately, as well as alcohol, Pitt still exudes cool out of every pore. He's also relaxed, happy to fill the allotted time with anecdotes of the evening before – but given the calibre of the film, this would actually be a waste. Killing Them Softly is a nasty, engrossing thriller that Andrew Dominik adapted from a 1974 novel, Cogan's Trade by George V Higgins. He transported it to 2008, to the global economic meltdown during the shift in power between Bush and Obama.

Pitt plays Cogan, a hitman who tries to do his job with minimum fuss to avoid the pleas and cries of his victims. Ray Liotta and James Gandolfini complete the cast of one of the most watchable mob films since 1995's Casino, but one that carries the underlying message that the Mafia is the darkest realisation of the American Dream; and it is as subject as anything else to the laws of economics.

This is the second collaboration between Pitt and the New Zealand-born Dominik, after they made the award- winning but commercially underrated The Assassination of Jesse James by the Coward Robert Ford in 2007. “Only about 12 people in the world saw that movie,” claims Pitt, but it's still one of my favourite ever films. We were in the trenches in that film and you bond in a trench, so we wanted to work with each other again.“

He says he loves the character of Cogan, describing him as “the clean-up man. I put things back together when they need to be put back together. I am The Enforcer.” Is he The Enforcer in real life, at home with his fiancée, the actress Angelina Jolie, and their children?

Pitt laughs. “No, I think I am the absolute opposite to this character, who's a complete pragmatist and doesn't want to feel emotion. That's why he describes murder as ”killing them softly“ – he doesn't want the human mess that comes with violence.

“For me, being a father has changed everything for me as far as perspective and interests go. I just want to take care of myself and be around them.”

Cogan certainly isn't the kiddy-friendly kind – and Pitt says he never brought him home with him. “I've heard these rumours that I stay in character the whole time during filming. It's not true. I'm not that kind of an actor. I'm always too happy to go home.”

With a brood of children so large they could be rented out to Steve Martin's Cheaper by the Dozen films, Pitt has proved himself to be a besotted father to the couple's three biological and three adopted children. He says happily that the highlight of the week was watching one of his four-year-old twins swim a length of the pool.

And despite telling reporters in 2011 that, if not totally retiring aged 50, he wanted to get behind the camera and produce, he now says he's changed his mind. “It's too much effort, it's too big a job. I'd rather be a Dad. It's more fun.”

It would be nice to think that in Pitt's slightly hazy, expansive frame of mind, one might be able to prise a wedding date out of him and thus have the scoop of the year – but one reporter already tried that, and was rewarded with a lazily amused, “Who do you think you are, schmuck?” look. After seven years and six children together, Brangelina became engaged earlier this year. Perhaps the most unbelievable of stories spun after the announcement was the one of how Pitt had become a Bridezilla in organising the wedding, fretting over confetti.

Rumours were rife during the summer that the wedding would be at the couple's chateau in France; now, those reports have switched to Richmond in London, where they have been based while Jolie films the fantasy drama Maleficent. In her absence, Pitt has been watching a lot of sport.

“We've had an amazing summer in London,” Pitt enthuses. “Even with the rain. We've had the Euro Cup, the Olympics, the Paralympics, Andy Murray at Wimbledon, it's been an incredible experience. Britain's certainly been good to us.”

And, in return, could they give London the Jolie-Pitt nuptials, ideally with George Clooney as best man? “George doesn't like institutions,” Pitt smiles. “Perhaps he could show people to their seats.”

For all we know, they might have done it already, in a July downpour at a Richmond registry office, overlooked by the press. The couple have, however, maintained they won't make a commitment until gay marriage is allowed in the USA – and for this to happen in the near future depends on Obama's re-election in November. “I'm a supporter of Obama,” Pitt declares, adroitly avoiding the issue of his own mother, Jane Pitt, recently stating that she supported Mitt Romney for espousing heterosexual-only marriage. “Gay marriage is only a matter of time. The next generation, they get it. It will happen.”

With its news montages and speeches from the US election of 2008, Killing Them Softly is released in the run-up to the next election, a move that Pitt describes as “a clever marketing tool”.

“I don't want it as a commentary on anyone's performance,” he adds. “It's a satirical film and it's by no means showing the whole of America. It was born of a cultural jaundice.”

But Dominik's deeper commentary on the dark heart of greed is unmissable, especially when Pitt as Cogan delivers the most striking line of the film: “America's not a country, it's a business. So pay me, motherfucker.”

“It's a compelling argument,” agrees Pitt. “I don't think by any means that that is all America is, but we are capitalists. There's the ideal of who we think we are as Americans, and there's the disconnections between our ideals and our motivations. Crime is just unvarnished capitalism, after all. And when the world is brought to the brink of catastrophe, then yes, I do think we should look at America as a business.

“We have had personal experience of the recent problems, making this movie,” Pitt continues. “After we made Jesse James, everything seemed to be about money. We really struggled to get anything made and this film was born out of that struggle. When Andy came to meet me about Killing Them Softly, it was the height of the financial crisis. It was the mortgage scam, a lot of people were losing their homes. Terrible, terrible times, and here is a story about those times.”

Even more poignant, Pitt recalls, was to set the film in New Orleans, the victim of both Hurricane Katrina and the financial crisis, where he and Jolie have a house. “What we needed was Failing City, USA,” he says, “and so I suggested it as of course we have a personal connection. They have a wonderful infrastructure for making films and anytime you bring a movie there, they are so grateful. It's a personal satisfaction to me to be able to create jobs.”

Creating jobs, donating money to Haiti, playing with his kids, making movies with a message. If only Brad Pitt was the kind of guy who'd occasionally throw a tantrum over confetti.

“I'm sorry, I was rubbish today,” he says on his way out. Killing me softly.

'Killing Them Softly' is released in the UK on 21 September

This article will appear in the 15 September print edition of The Independent's Radar magazine