Why isn’t Jason Clarke more famous? He’s very good in lots of big films. He’s smart, cheery and handsome, with a slightly cracked aspect round the eyes that means evil also comes easy. Keira Knightley, twice his screen wife, emails to say: “I totally love working with Jason. He is one of my favourite actors. His work is always complex and nuanced. It is a joy to be his sparring partner.” Yet when you tell people his name, confusion flickers over their face.

The first clue comes as he sits down. The son of a Queensland sheep shearer, Clarke carries himself with the casual bagginess and vague impatience of a holidaying history teacher. He wants to use our half-hour not to promote movies but to better understand Brexit (“You guys are stabbing yourselves in the foot!”) and to recommend non-fiction audiobooks narrated by “old English dudes”.

“The one on Peter the Great – go get it! – has this wonderful little biting playfulness. To listen to all the wars and the revolutions and death and murder and dwarves and drunkenness and tsars and tyrants read by this witty Englishman, it makes it very enjoyable.” He chuckles, legs stretched, hair like a haystack.

Clarke, 49, has been studying Russia recently in aid of Catherine the Great, a Sky series in which he stars opposite Helen Mirren. Before that, he was knee-deep in Antony Beevor as prep for The Aftermath, a tragic romance set in Hamburg just after the second world war. He was particularly shocked by the Red Army’s treatment of German women and girls, some of whom were raped “not just five or 10 times but 50 or 60 times,” he reports. “Holy moly. My God, the Germans suffered. But it’s not talked about.”

The Aftermath aims to give it airtime, while foregrounding the story of two Brits – Lewis (Clarke), a soft-spoken colonel, and Rachael (Knightley) – who move into the mansion of Alexander Skarsgård’s ominously hot German architect.

Clarke was curveball casting for Lewis, concedes director James Kent. But he liked his “primal, peaceful realism” and his “probably Australian quality of pure, uncluttered, unfussy truth. Lewis has been battered and bruised by five years of conflict,” he says, “turned into something rougher and tougher and dehumanised. Jason loved all that.”

He did, Clarke confirms. Especially the erotica – or, for his character, the lack of it. “Lewis is frightened,” he says. “I think a lot of these men were. The power of intimacy when you haven’t had it. He’s confident with a lot of other things but with his wife he’s terrified. I love the way they showed that sexuality.”

For Knightley, the film is an exploration of “the way men and women communicate and grieve”. She believes there’s a key difference: women need to speak about the dead, while “men need to put their emotions into work”.

Clarke disagrees. “If we both watched somebody blown to bits, the trauma and empathy and fear and anger is going to be pretty shared.” He looks pragmatic. Would he be a fighter? Of course, he says, though engagement today is “a lot more complicated than it was during world war two, when there was a moral certitude”.

A dose of transparency is what Britain today needs, he thinks. America – where he now lives with his wife and their two children – may be shaky, but “it’s all coming out. A lot of it’s tough and horrible but the debate is open, and the whole world comments. More so than on their own country.”

Snobbery? “Of course. It’s easy to point at a bad guy over there.” Clarke loves his adopted homeland, calls it “a problem-solving country” to whom we owe an enduring debt. “Europe has a big responsibility for war,” he says. “And a propensity for it, too.”

Clarke often plays if not actual soldiers then part of a quasi-military squad on a real-life mission: up the north face in Everest, to the moon in First Man, round Afghanistan in search of Osama Bin Laden in Zero Dark Thirty.

“He’s a highly intelligent alpha male,” says Kent. “If you were on a mountain, he’d really know which ropes to use.”

And it’s this hearty machismo which makes it curious that in both The Aftermath and Clarke’s other film out on Friday, he’s the third wheel: a lumpen gooseberry in big steamy pudding. But unlike The Aftermath, Serenity is no credit to Clarke’s – or anyone else’s – CV. He plays Frank, a moneybags criminal who abuses his wife (Anne Hathaway), beats her son and still finds the energy to visit dockside child prostitutes. “I’m gonna fucking head up there tonight and grab myself some of that $10 ass,” he informs Matthew McConaughey’s usually-nude tuna fisherman.

Reviewers have detected a self-awareness in Clarke’s performance absent from the rest of this appalling trash, but it’s still an odd choice for a project, however much he wants “a pay cheque and an exciting life” (Serenity was shot in Mauritius).

Can some films feel thin, once you’ve been gorging on the Romanoffs? He nods: especially if there’s a lot of greenscreen. “All of a sudden you lose your confidence, if you’ve got to talk to a bit of a string with a red dot on it for 10 minutes.”

The most CGI Clarke encountered was on what should have been his blockbuster breakthrough: Terminator Genisys. But rather than rebooting the franchise, the film essentially ended it. Scan back through Clarke’s career and he starts seeming a bit unlucky. Projects that looked like Oscar dead certs – First Man, Everest, his Ted Kennedy film, Chappaquiddick – all failed to launch.

Plus, says Kent, he’s different in all of them: a character actor who looks like a lead. “He gravitates to range. Maybe the public don’t have an easy grasp of who he is in the same way they might with someone who slightly repeats roles.” For instance, “I think it’s clear what Benedict Cumberbatch is. He’s clearly somebody who plays offbeat outsiders, highly intelligent in a sort of Sherlocky way. Obviously he has much more range than that; but with The Imitation Game and Dominic Cummings, there’s a sort of pattern there.”

Clarke has little interest in such issues. He wants to know what the hell we’re playing at leaving the EU. “London has been the capital of the world, more so than New York, for much of my lifetime.” What he’s seeing in the city today, he says, is “pretty scary for everybody on a deeply ethical level about what democracy is”.

I jibber that the debate was full of confusion and obfuscation. That many leavers may have been more concerned about immigration than Brussels. “That’s just weird,” he scoffs. “You’re going in for brain surgery when actually what you’ve got is a bad ankle. Now what looked like a pothole has turned into the Grand Canyon. And you’re concerned about America?”

• The Aftermath and Serenity are out on 1 March

• This article was amended on 8 March 2019. An earlier version included a reference saying that “70% of German women were raped by the Red Army”. That was said by Jason Clarke in error, and has been removed.