WHEN countries talk about their national treasures, they usually refer to people with a big dose of cute and cuddly about them. So on the surface, Peter Mullan bucks the trend. I’d argue that the Glaswegian actor and director is a Scottish national treasure, a vital creative force for a quarter of a century. But rather than make us feel all warm inside, Mullan has a habit of putting us through the mill.

Last week this most truthful of actors was the dominant presence in the adaptation of Sunset Song, as the tyrannical father of the story’s heroine. It was the sort of performance we most associate with him, mining the darker, scarier parts of human behaviour.

But now he’s front and centre of a film – less grand than Sunset Song, but no less resonant – that allows him a rare chance to play someone decent, honourable and life-affirming. In that sense Hector is a throwback to Mullan’s breakthrough film, My Name Is Joe in 1998, where he also played a character who retains his humanity despite hardship; I think this is an equally spectacular showcase of his skills.

Hector is a peripatetic homeless man, who travels endlessly up and down Britain’s motorways, stopping over at service stations where he uses the facilities to clean himself up, sit in the warm, recharge before again hitting the road. He draws a meagre pension, which keeps him from starving. But often nights are spent under cardboard boxes, and his gammy leg struggles with the miles on foot in between rides and the often bitter cold of life outdoors.

All the while, this indomitable man keeps clean and tidy, is polite to a fault and grateful for any display of generosity or kindness. And he’s clearly intelligent. So the question, as so often in life, is how did he get here? What happened to him?

Writer and director Jake Gavin keeps the answer to that till the end of his confident first feature. Hector’s homeless companions accept that they’re not going to learn much about him, whether his life story or the nature of the illness that will require him to have an operation. In the meantime, we follow Hector on a winter journey from Glasgow to London, to the same homeless shelter where he spends every Christmas. It’s an arduous trip, not one we feel confident he will survive. Perhaps he feels the same, because en route he decides to call in on his past.

Homelessness is a perennial and important issue, one with bitter realities that could make for difficult, discomforting drama. That’s one worthwhile route, but Gavin offers something else. Though he fills his film with the details of the day-to-day of homeless life – the practical needs, physical and mental problems, very real dangers – he’s nevertheless made a character-driven and essentially hopeful film, whose positive notes rest on the spirit of its central character.

With his white beard and gleaming eyes, and an acting style that is peerlessly naturalistic, Mullan makes Hector charismatic and likeable, at once believable and mysterious, in that way that people who have walked out on their entire lives are inevitably mysterious. Even as revelations turn the film towards a more familiar track, Mullan keeps its course true.

A nice supporting cast includes Keith Allen, Stephen Tompkinson and Gina McKee. But other than its star, the most significant impression is made by the director, who lends a social realist storyline elements of road movie and Christmas fable. The result has tragedy, pain, folly and foible, and real heart.

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