Aki Kaurismaki refuses to make a digital film: 'I am a filmmaker, not a pixel-maker.' "Of course, the working class is not such a sexy and commercial subject, I understand from the popcorn audience," Kaurismaki says drily. "But I couldn't write dialogue for upper-class people because I wouldn't know what they say. I don't know if they talk at all. Maybe they are just shopping. And selling and buying stocks. Stocks and stockings. I find rich people boring." In his new film, The Other Side of Hope, we find ourselves once again with the Nordic proletariat: in this instance, the indolent staff of a visibly awful restaurant. They clearly don't care two hoots about their customers, but they do step up to help and hide a Syrian refugee they find sleeping behind their rubbish bins. This is how people in Kaurismaki's films are saved: one at a time, by the kindness of strangers. Beneath that romantic humanism, however, Kaurismaki harbours a very specifically political anger. The Other Side of Hope is the second film he has made about refugees in Europe, spurred by the Finnish government's response to a sudden surge in arrivals from Syria. "The government started to kick them out as fast as possible," he says. "I wanted to get this film made because for me this is so shaming for Finland and for Europe. A shameful way of treating your neighbours. So I skipped all artistic ideas. I just wanted to tell a story about this subject."

Of course, the rejection or incarceration of refugees is by no means just a Finnish problem. "Australia is quite famous too, in a bad way. And this Finnish government is much the same, splitting up families, saying mothers and babies must leave while the fathers stay, this kind of nonsense. Finland is lacking people; people are getting old and the country will need young people who want to work but when they come, they are thrown out. "So first of all, this is a bad mistake. Secondly, they can't change it anyway. When the climate change really starts, then people have to move and they won't even ask if they can come, they will just come. So why panic with this minimal number of people?" The Other Side of Hope follows two stories. One begins in the hold of a boat, where a pile of coal shifts to reveal the amiable face of Khaled (Sherwan Haji); when he emerges on to the Helsinki dock, a blues singer playing a home-made junk guitar – one of Kaurismaki's endless cavalcade of muso mates who help give his films their eccentric verve – advises him on where to wash his face and where to register as an asylum seeker. It is the start of his cat-and-mouse game with the courts, the police and the hostel where he is sent to wait for a hearing and an attempt to find his sister who, if she is alive, is the only other surviving member of his family. At the same time, we follow sad sack Waldemar (Sakari Kuosmanen), a salesman (like Kaurismaki's own father) with an alcoholic wife; he throws in the towel, sells all his stock, makes a small fortune at a card game and uses the money to buy a failing restaurant, The Golden Pint. He is full of ideas to jazz it up. One night it's lounge music; another night he decides sushi is the answer and gets all the staff to wear karate outfits. By that time they have adopted both the fugitive Khaled and a dog who is living illegally, rather like Khaled, in the kitchen. Kaurismaki fans will have been waiting for the dog; as one reviewer wrote, even if he made a film on Mars there would be a cute dog in it somewhere.

"This is my sixth dog and all of them have been acting: it's a sort of tradition," he says. He may say he forgot about aesthetics, but of course that would never be true for someone as steeped in the masters as Kaurismaki is. "From the Lumiere brothers to the early '60s I saw everything; Bunuel is my god and so on," he says. Haji says Kaurismaki was quite happy to entrust him with his speeches in Arabic, asking only "did you say everything?" before moving on to the next shot. But he could also obsess over details, stopping one scene mid-shoot because he wanted the background wall to be painted a slightly different colour. And there is no mistaking his visual universe, pitched somewhere between the present and the 1950s. His bureaucrats use manual typewriters. The shops use lovingly preserved adding machines. "That's totally aesthetic," he admits. "I don't like modern cars. They are ugly for me. The same goes for all the other machines. Using modern sets is not for me, or they have to be absolutely ultra-modern. I think reality kills film." And when he says film, that's what he means; he says he'll be forced into a leisurely life of mushroom-picking when the owner of the Belgian laboratory that develops his 35mm film retires in 2021. He considers that the deadline for his last film.

"I will die with my boots on. I won't make a digital film in this life," he told one interviewer. "Cinema is made from light. I am a filmmaker, not a pixel-maker." The real world of these vintage office machines was one where most progressives were convinced that racism was inexorably disappearing. If you had said in 1970 that there would be a new Fascist party in socialist Finland, nobody would have taken you seriously. Does he feel disappointed in humanity? "I never had very high hopes of humanity," he counters. "I had hope 20 years ago, but not now. Greed will kill us – and maybe that's OK for the planet. Because it all goes back to money. Everything goes back to money." And yet he ploughs on, with his stirring Finnish mix of optimism and pessimism, humour and melancholia. What else can he do? "Cinema can't change much," he says. "But it can certainly reach some people and change some opinions. You can only hope." The Other Side of Hope opens on March 29. Advance screenings will be held March 23-25.