Inside the glass-fronted office that is home to Pearl Street Films in Santa Monica, visitors are greeted by its owners, if not always in person then by their screen alter egos. In one corner stands a life-size mannequin wearing Matt Damon’s spacesuit from The Martian. There, glowering nearby, is another in Ben Affleck’s bat suit, complete with mask, pointy ears and a flowing cape. “What’s the good of doing a movie with great souvenirs if you don’t get to keep them?” deadpans Affleck.

Damon and Affleck, Boston boys, best friends since childhood, have done good. Their production company also has an impressive track record. Pearl Street co-produced Damon’s last Jason Bourne movie and Affleck’s latest, the gangster epic Live by Night. It is behind the Oscar-tipped drama Manchester by the Sea, starring Affleck’s younger brother, Casey. Damon, in an interview with this magazine last year, joked that Affleck, now an Academy Award-winning director, always keeps the best roles for himself. “That’s true,” Affleck laughs. “But I’d love to get a great two-handed script and do a movie with Matt. But, for whatever reason, those scripts are rare.”

He’s sprawled on the sofa dressed in blue jeans, trainers and grey sweatshirt. He sports dark stubble that blurs the chiselled jaw that matches his sportman’s physique. Though instantly recognisable, he still rises from the sofa and offers a firm handshake and an unnecessary but polite, “Hi, I’m Ben.”

Two of a kind: with best buddy Matt Damon in Good Will Hunting. Photograph: Miramax/Sportsphoto Ltd/Allstar

While his blockbuster films – such as Gone Girl and Argo (which he also directed) – have been watched by millions, his American TV appearances are also worth searching out. He sounds off on the HBO sports show Any Given Wednesday, effing and blinding like a bricklayer who’s just dropped a bag of cement on his toe. He’s equally at home slugging it out round for round with intellectuals and politicos on the current affairs programme Real Time. He’s as passionate about the injustice meted out to one of his favourite football players as he is about comments that veer close to Islamophobia.

“I love a good debate and I get very energised by it,” he says. “On Real Time, I think people could tell I had a genuine emotional response because I strongly believe that no one should be stereotyped on the basis of their race or religion. It’s one of the most fundamental tenets of liberal thought.”

Affleck grew up in a tough Boston neighbourhood and if someone picks a fight, he’s not about to back down. You can’t help thinking he’d have a head start if he ever thought of going into the pugilistic world of American politics. “But I really wouldn’t want to,” he says. “It’s not because I think being a public servant wouldn’t be satisfying, but it’s become a pure money-raising exercise from beginning to end. It’s small talk with people who you want to squeeze money out of. It’s sleazy. You have to have a certain tolerance to that kind of schmooze that I don’t have.”

Making a stand: in the psychological thriller, Gone Girl. Photograph: Allstar/New Regency Pictures

Talking of world-class schmoozing, it’s just weeks before Trump’s inauguration and Affleck is still trying to come to terms with his victory. He saw the signs in the US and the UK of populism on the rise. “I spent five months in London [last year] and I have to say the Brexit vote smacked of the same kinds of things I heard here. People whose overarching political agenda is that immigrants are ruining things for us or immigrants are getting one over on us somehow, taking advantage. In London, it’s Polish people and here it’s Mexican Americans. I still believe in the basic goodness of people, but that doesn’t mean we aren’t going through a spell where we’re in thrall to some ugly ideas and ugly notions.”

It’s unlikely that an invite to the Trump White House will be landing on to his doormat anytime soon. “I met him once at a Fashion Week event in Milan. You knew you were at a cheesy party if Donald Trump was there. He would kind of trawl around them. He was famous for only granting permission for films to shoot on his real estate locations if they put him in as a cameo. The director Marty Brest told me he’d had to create a whole hand-shaking scene in Scent of a Woman where Trump comes out of the door and goes, ‘Hey! Donald Trump, nice to meet you,’ as he bumps into Al Pacino. The ego was there a long time ago.”

Affleck’s own ego is more than satisfied with acting and directing. With Live by Night, based on a Dennis Lehane novel, he does both. He plays Joe Coughlin, a corrupt policeman’s son who runs with the bad boys in 1920s Prohibition Boston and falls for the girlfriend of his ruthless boss. When the boss finds out about their affair, Coughlin is lucky to escape with his life. He moves up the ranks with a rival mob, overseeing a rum-running operation.

‘I always tried to treat other people well’: with his estranged wife, Jennifer Garner. The couple have three children. Photograph: Broadimage/Rex

Affleck describes the movie as a love letter to the gangster flicks of the 1930s and 40s, and with a reported budget of $65m it’s his biggest movie to date. The era of fedora hats, braces and brogues fits Affleck’s classic matinee idol good looks, too. The first act is, once again, set in Boston just like two of his earlier films as a director, Gone Baby Gone and The Town. “I think you recognise what’s closest to home,” he says. “Wherever you were raised and formed your primary attachments and learned about life, that’s the world that’s most accessible to you. Dennis really gets Boston. He infuses his story with a love for the place, even if parts of it aren’t that lovable.”

Although Affleck was born in California, his family moved to Cambridge on the outskirts of Boston when he was two. His father, Timothy, went from one job to the next – bartender, mechanic, janitor and, later, after battling alcoholism, an addiction counsellor. His mother, Chris, was a teacher. They separated when he was 12. “I guess contemporary helicopter parents would be aghast at our level of supervision, but it wasn’t bad. There were scary kids and people that you’d want to stay away from, but I tried to make people laugh and make friends.”

His best friend, then and now, was Damon, two years older, who lived a few blocks away. They began acting at high school and as teenagers would go to auditions together. Damon went to Harvard and Affleck to the University of Vermont, but both dropped out and headed to Los Angeles to “live the dream”. “It was me, Matt, my brother Casey and a bunch of friends from Boston – all of them were trying to make it in some capacity or other. It was a time to experiment, to go to auditions and try stuff. And part of what we revelled in was the absurd level of frustration that we went through and the ridiculous hoops we had to jump through. Those years were wonderful – they were great, formative, blissful, fun, free years.”

It was during those struggling years that he made his low-budget directorial debut in the insanely titled I Killed My Lesbian Wife, Hung Her on a Meathook, and Now I Have a Three Picture Deal at Disney. “Yeah, the title is the best thing about it,” he says. “It’s about how we sometimes forgive the lunatic behaviour of artists and call it “eccentricity”. I was trying to make it as an actor and hearing stories of how ‘so and so was doing this’ or ‘that guy has this outrageous technique’. And I remember thinking, “What bullshit.” Just because this guy’s on some crazy diet doesn’t make him talented. The work itself is what matters.” Sound advice that he, perhaps, should have remembered.

We can be heroes: as Batman, opposite Henry Cavill in a scene from Batman v Superman: Dawn of Justice. Photograph: Clay Enos/AP

In the early 2000s he made a series of disastrous film choices including Michael Bay’s overblown Pearl Harbor and the dreadful weepie Jersey Girl. At the same time, he became engaged to Jennifer Lopez and there were reports of drinking, gambling and a spell in rehab. “I’d always had a strong idea about my values and the direction I wanted to be headed in, then I ran into getting famous and it totally spun me around and I flailed around for a few years. When you’re a young man in your 20s, part of that is making mistakes and learning from them. I just made those in front of everybody, rather than privately. There’s stuff I look back on and kind of cringe at but I always tried to treat other people well. My parents imbued that in me and the mistakes I made were mostly just of the embarrassing kind.”

The upswing in his professional fortunes coincided with the start of his relationship with the actress Jennifer Garner, the mother of his three children, Violet, 11, Seraphina, 7, and Sam, 4. “I think becoming a father makes you see the world differently and it’s good.” In 2015, he and Garner, his wife of 10 years, announced they were separating, although both insist they remain on good terms, despite the tabloid headlines claiming the split involved the couple’s nanny.

The poster for Live by Night has the tag line “the American dream comes at a price”. He agrees it’s pertinent to his own life. “Absolutely. I’ve been lucky. I’ve had my wildest dreams come true, but the price is the Faustian exchange you make where your identity is not your own. You become a public figure and it changes all the rules,. The press can become invasive and dishonest, and you have to put up with inconvenient stuff like that. I’m at peace with paying my own price, what I’m not at peace with is when it invades on my kids’ space and time. They didn’t make any bargains. I try to shelter them as best I can. That’s my only real gripe.”

Essentially, he insists, he’s the person he was before he won his Oscar for the Good Will Hunting script back in 1998. He credits Robin Williams with getting the film into production. “Most people can’t point to the moment that changed their life in such a dramatic way, but I can. It was the moment that Robin decided to take a flyer on that movie. I’ll always feel a huge debt to him although now I’ll never get to repay it.” Williams, who had dementia, took his own life in 2014. “It’s one of these incredibly horrible diseases that destroys the mind and that was especially cruel to a guy like Robin who was always so brilliant and quick witted. And on a totally selfish level, he’s the reason why I got successful in this business. If Robin hadn’t done Good Will Hunting, Matt and I would still be sitting there today talking about how we could update that script.”

Instead, they’re sitting in their office, talking about other people’s scripts and their own film projects. Though the batman costume in the foyer is from Affleck’s caped crusader in Zack Snyder’s messy Batman v Superman: Dawn of Justice, word is that he will get to direct his own superhero movie, tentatively titled The Batman. “That’s the idea. But it’s not a set thing and there’s no script. If it doesn’t come together in a way I think is really great I’m not going to do it.”

Ask him why he took the Batman role and he replies with characteristic honesty that he did it for his son. “Sam thinks his dad is Batman,” he laughs. “That’s an incredible feeling.” Everyone wants to be a superhero to their son, although it strikes me that one of the best things about Affleck is that he remains endearingly human.

Live By Night is released on 13 January