Tyrannosaur, Paddy Considine, 91 mins (18)

He's a drunk who's just kicked his dog to death; she's a troubled Christian with a secret – Paddy Considine's directorial debut is my kind of film!

Regular readers of this column might have noticed that words such as "bleak", "harrowing" and "unforgiving" crop up with regularity – usually as recommendations.

I admit I tend to favour work of a melancholy hue, and have recently encouraged you to rush out and see films about the end of the world and the woes of Chilean morticians. But there's a reason for this.

It's just that, these days at least, films of a downbeat disposition are more likely to be distinctive and, above all, honest. Film-makers after a quick buck are well advised to hit the happy notes, as a relentless stream of mechanical romcoms proves. "Feelgood" has become the default mode of the cynic. But few directors ever got rich purveying the authentically sombre – so any who choose to dwell on darker matters are quite likely to be showing some integrity at the very least, regardless of the work's quality.

Of course, I've sat through some gruellingly inept testaments of doom, and equally I'll welcome any genuinely euphoric movie with open arms. But meanwhile, here's an unapologetically downbeat British film, and one that feels absolutely for real. Tyrannosaur is the first feature by actor Paddy Considine, who has played several moody hard cases in his time, but also has a penchant for goofing around, most recently as the idiot guru in Submarine. As a writer-director, though, he's to be taken very seriously. An expansion of Considine's 2007 short Dog Altogether, Tyrannosaur stars Peter Mullan as Joseph, an embittered, violent drunk whose closest relationship is with his dog – not that that stops him kicking the mutt to death early in the film.

From the start, we know that Tyrannosaur – while ostensibly in the mainstream of hard-tacks British realism – is effectively set in hell. Opposite Joseph lives a neglected young boy whose mother's thuggish boyfriend also has a dog, which he delights in using to terrorise the poor kid. This is a world in which brutality is a constant.

Even so, Joseph – carrying a burden of guilt and shame along with his rage – seems to find tenderness when he stumbles into a charity shop run by Christian volunteer Hannah (Olivia Colman). Seeing his desperate state, she offers to pray for Joseph, and her concern seems for a moment to soften him, although he's soon making her the target of his sour contempt.

Joseph has Hannah down as a wet do-gooder, with her Home Counties diction and gentle piety – but the moment we see her in her suburban home, nursing an extra large glass of red, we know something's wrong. And when her husband James (Eddie Marsan) enters to find her asleep on the sofa, we discover what that is. This revelation of Hannah's own calvary is done in a single shot, with chillingly delicate understatement – making it the most horrific thing in the film.

As one world of personal pain connects with another, Joseph finds himself offering shelter to the woman he thought was sheltering him. Things build up to a shock reveal – although it's more of a shock for Joseph than for the viewer, who's likely to be way ahead of him. There's a redemptive conclusion, after a fashion – although it's so far from what you'd normally call a happy ending, it's truer to call it a clearing of the air.

Sparely scripted by Considine, the film is steeped in oppressive atmosphere – cramped, box-like interiors evoke a milieu not unlike Andrea Arnold's, but with a more crafted expressionist slant. In the exteriors, as shot by Erik Wilson, even the daylight is grey, decrepit, as if it's had the life-giving qualities bled out of it.

Not everything convinces: acoustic guitar music hits the pathos button too directly, while a pub ballad about strength through adversity too obviously reassures us that there's light at the end of the tunnel. But Considine's overall control keeps the film riveting, and so, above all, does the acting. Mullan is superb, but you expect him to be: he specialises in hard-bitten wrecks. Eddie Marsan is good too, although the role doesn't stretch his limits; we're more than used to seeing him as a weak man with a short fuse.

But the out-and-out revelation is Olivia Colman. We know her larking around in television comedies like Peep Show and Rev, but here she plays it straight as a figure of intense vulnerability, strength and dignity. The film takes Hannah's faith seriously, but also sees what it protects her from: not least, herself. Colman captures the demeanour of a victim in chronic denial – walking arms folded, apologetic, as if to take up less space in the world. By the time the cracks begin to open, and Hannah starts to show her own fury, you realise that this is a very considerable performance indeed.

This insightful film has a serious but understated (and bleakly witty) theological slant: "God still thinks he's God," Joseph comments. "No one's told him otherwise". Tyrannosaur inhabits a closed-in atmosphere of desolation – though not despair – that some will find compelling, others oppressive. But it's a confident, honest work that touches a raw nerve. As they say in the blurbs: "Bleak, harrowing, unforgiving – go see."

Next Week:

Jonathan Romney investigates weird sex, Australian-style, in the Jane Campion-endorsed Sleeping Beauty

Film Choice

Kirsten Dunst and Charlotte Gainsbourg gird themselves for the end of the world in Melancholia, the bizarre, beautiful, Bergmanesque apocalypse drama from Lars von Trier. Meanwhile, real-life catastrophe, of a more comic variety, comes in Cane Toads: The Conquest, Mark Lewis's 3D revisit to his docu about the batrachians eating Australia.