Tim Roth: who's the daddy?

When Clarice Starling is first assigned to interview Hannibal Lecter in The Silence of the Lambs, we are told, in Thomas Harris's novel, that "a brief silence follows the name, always, in any civilised gathering". Something similar happens when you say you're off to interview Tim Roth. A light gasp, a small step back. Roth – who was set to play the younger Lecter in 2002's Red Dragon, until Anthony Hopkins dyed his hair and reprised the role – has a reputation for being slippery. He just doesn't give, I'm told. Meet him in California, people caution, and he clams up. Get an audience in London and he is prickly, defensive.

So why is it that in Cannes, at least, he couldn't be sweeter? Roth is warm and friendly; he has the guttural chuckle of an ageing rocker. Cannes makes him happy. Here there are no particular national- or class-based expectations. He doesn't have to be the scrappy skinhead of Alan Clarke's Made in Britain (1982) or Stephen Frears's The Hit (1984) – although he will admit to hamming it up off-screen at the start of his career, in order to fit such parts. It doesn't matter that he is, in fact, the relatively affluent son of a journalist; his father changed the family name from Smith to Roth in 1944, an act of anti-Nazi solidarity ("I get invited to an awful lot of Jewish functions," Roth says).

In Cannes, he is simply a cineaste, and a Croisette staple of 20 years standing. Roth has made a splash here as an actor, with Quentin Tarantino's Reservoir Dogs and Pulp Fiction, and as a director, with The War Zone, in 1999. This year he is president of the judging panel for the festival's Un Certain Regard competition. His new film, Broken, by first-time director Rufus Norris, was weepily received at its premiere the night before we meet.

There is another reason: for nearly a week, France has been officially socialist. "I think before the bubble bursts we should enjoy the notion," Roth says. "I think that just the word – socialism – is good for a while. It's the thing Obama is always being accused of by Fox News. If only! So, just for a second, it's nice to feel that Hollande might deliver on a couple of his promises."

He is disenchanted with British politics. "I'm sick of voting for the lesser arsehole." Roth lives between California and London, and the last time he voted, "I just looked around to see who wanted to do a proper job, rather than someone who wanted to bang the secretary. And also, I have to say, the whole God thing is starting to really piss me off. Blair's Christianity made me angry, and New Labour was a joke. I'm not sure if I'll vote for the new child who has taken over, because I wouldn't know how I'd be able to figure out if he was Cameron or not. They're all starting to look the same, these boardroom guys. They don't represent us, the country. They represent business and corporate wealth and greed and guns. They don't deserve our vote, any of them."

Those who might, Roth thinks, include the Green party (which he supported in the recent local elections), Tony Benn and, more surprisingly, George Galloway. "Maybe he will be something. He's definitely a smooth talker. Sometimes I like what he says." I'm quizzical. He pauses, then goes for a semi non-sequitur. "My dad was a Communist Party member who fought for his country. And I just don't think we lived up to his expectations."

Roth's new film, Broken, is about having the courage to seize one's personal and social responsibilities. It's the story of 11-year-old Skunk, a tomboyish schoolgirl who witnesses the assault of a man with learning difficulties by a widowed father; she is under the mistaken impression that this father has raped one of his three daughters. Skunk has an absent mother, too, who left her, her brother and her solicitor father Archie (Roth) shortly after Skunk's birth.

Seen alongside the other British films screening at Cannes this year (Ben Wheatley's homicidal caravan yarn Sightseers; Ken Loach's whisky heist The Angels' Share), you could draw some fairly bleak conclusions about the state of the nation. But Roth is eager to focus instead on what Broken has to say about more universal family concerns. As Archie, he is the film's moral centre: irreproachably well-intentioned, verging on the weak. It is Roth's most mild-mannered role in years; did he think Archie was too passive? "I prefer gentle. He's just a good man; I really rather love him."

Broken's plot turns on a broken mobile phone, but otherwise presents a world where technology is curiously absent. New media has exacerbated age-old parenting problems, Roth thinks. "Because it's not new anymore, and that's a gateway to potentially horrendous aspects of the world. You can give your experience only up to a point. And now it's just sweeping across the planet."

What's the effect? "A different kind of innocence. I think that happened with the advent of TV and that was only a few years ago, really. Cellphones have changed the world. I'm not saying it's necessarily a bad thing, [but] it's scary." He brightens, and gives one of those half-maniacal laughs. "But then we won't be around for too long, anyway. And the next generation will be scared about something else."

Roth has three sons – two teenagers with his wife, fashion designer Nikki Butler, and 28-year-old Jack from a previous relationship. On and off-screen, he has an easy rapport with Eloise Laurence, who plays Skunk ("She calls me her other dad. So does her dad"). Alongside Norris and Damon Albarn, who composed the film's soundtrack, and who both have children of a similar age, Roth formed a "creatively concerned parents' collective … it was like being a family on set, a ridiculously close experience. You hear that so many times about working on a film, and mostly it's not true."

He is now struggling with the fact his own children are growing up. "They don't need me the way I want them to. They're breaking all those bonds, and it's quite disturbing and saddening. This trying to handle their next part of the journey. And they're doing a bloody good job of it, all of them. It's magnificent, but it's difficult. It's so hard not to be loved in the way that they loved you when they were little."

For Roth, family relations and how well you handle them seem to be key. He returns to the subject of politics, putting it within the context of family. The think he likes most about Obama, for instance, is that he's married to Michelle. "I think he's a bit of a Republican. We're still in two wars, and he's only just come round to the notion of gay marriage. I don't quite understand what the fuss is about. I think he's very good on telly. But I think the fact he has a woman who seems to be as strong and as good as that is possibly a reason to vote  for him. I do sense there's a good heart there."

You sense there's a good heart in Roth, too. "Good luck, darlin'!" is his chipper farewell –and Hannibal Lecter never said goodbye to Clarice like that.