Does anyone actually love the films of Ken Loach? You can admire them. You can respect them. You can even be moved by them (Kes is the obvious example), but can you actually love them? Is there a couple — outside the ranks of the Socialist Workers Party — whose idea of the perfect Saturday night is to order in a pizza and cuddle up to the films of Ken Loach? His defenders would say Loach doesn’t make that kind of film: his work gives a voice to the marginalised, a face to the unseen. But lots of film-makers are doing that, mostly in the documentary format, and they’re making movies people love. Just ask Michael Moore.

The problem with Loach’s more overtly controversial films — a good example is 1990’s Belfast-set Hidden Agenda — is that once the controversy they provoke dies down, the film tends to die with it. I suspect this will be the fate of The Wind That Shakes the Barley. This year’s Palme d’Or winner at Cannes, it is a triumph of controversy over artistic content.

Set in Ireland in the 1920s, it is about a small band of Irish Republican Army fighters engaged in a guerrilla war against the British occupation and, in particular, against the Black and Tans, a brutal special force sent to crush the move towards Irish independence. Damien (Cillian Murphy) is a doctor heading off to work in London when, having witnessed the casual violence of the Black and Tans one time too many, he decides to join a local IRA unit that includes his brother, Teddy (Padraic Delaney). They steal guns, shoot traitors and kill British soldiers. Then the republican movement is split when a treaty is signed, under which the British give the Irish partial independence, and these brothers in arms turn on each other.

As a critique of British imperialism, The Wind That Shakes the Barley makes Mel Gibson’s Braveheart look complex and nuanced. Isn’t it curious that the Loach crowd are the first to sneer at the simplistic good guy/bad guy world-view of the typical Hollywood blockbuster, but admire it when its target is the British Establishment? Here there are no shades of grey. There are good guys (IRA) and bad guys (the British), and when the good guys do bad things, they are still good guys because they kill people and feel guilty about it. Even in the second half, when the bad Brits depart, the good guys divide neatly into goodies and baddies, the latter being those who support the deal with the British.

Of course, Loach could make the valid point that there was no good side to the Black and Tans. But we could have done with a little more psychological insight into these men. The one attempt to understand them is when Damien is being interrogated by a British officer and complains of their brutality. The officer says: “What can you expect of men who have been through the horror of the first world war?” This raises an awkward question for Loach: were these men also the victims of British warmongering? The Wind That Shakes the Barley has already provoked a lot of debate about its historical accuracy and the political points Loach and his screenwriter, Paul Laverty, have set out to make. But little will be said about the film as a drama; on this level, it is an utter failure. In Loach’s eagerness to show British imperialism at its worst, the viewer is subjected time and time again to scenes of harrowing brutality: beatings, a prisoner having his fingernails torn off, numerous executions. All this violence turns you away from the film and the lives within it. But what is missing is living, breathing characters. Somewhere in this polemic, real people are trying to get out and be part of the story, but they are always being pushed aside by Loach’s political points. Their relationships never come to life.

For example, there is the obvious conflict between the two brothers: we never feel the tragedy of their division because we get no sense that they had a relationship. Even the film’s central romance, the relationship between Damien and fellow activist Sinead (Orla Fitzgerald), feels tacked on.

In interviews, Loach has stated that there is a link between the occupying US force in Iraq and the British occupation of Ireland. But that parallel is utterly facile. For all the terrible things the coalition forces have done there, they are no Black and Tans. If Loach had stopped waving his red flag, perhaps he would have made a better film.

The Wind That Shakes the Barley, 15, 127 mins, Two stars