Reviewed - The Wind That Shakes the Barley: Ken Loach tackles the brutal founding of the Irish State in a drama that wears its politics on its sleeve, writes Michael Dwyer

Already the subject of vigorous debate among those who have seen it, and the target of wildly extreme allegations by some who haven't, Ken Loach's thoughtful, powerful and moving Irish political drama achieved unanimity among this year's Cannes Film Festival jury, who gave it their highest prize, the Palme d'Or.

Throughout his remarkable career, Loach has been one of the most egalitarian, obstinately uncompromisingly and socially and politically concerned directors working in world cinema. The Wind That Shakes the Barley marks his sixth collaboration with Scottish lawyer-turned-screenwriter Paul Laverty. It is, unsurprisingly, politically loaded.

Having tackled the Spanish civil war in Land and Freedom, Loach and Laverty explore the turbulent events in early 1920s Ireland, during the War of Independence and the subsequent Civil War. The experiences of a rural Cork guerrilla force of flying columns serve as both a microcosm and the dramatic conduit in a film where the recurring, twisting theme of taking sides is evident from the innocuous first scene of a hurling match.

There's no doubt which side Loach takes. The Black and Tans are depicted as callous, belligerent oppressors, and there is, perhaps, one scene too many to emphasise their sadism. The film proves more complex than that on just about every level, however, and a later scene observes them from a socialist perspective, as servants of their political masters, as men hardened from years up to their necks in muck and vomit in the trenches of the Somme.

It's more complicated on the Irish side, and even more so when that side is splintered. Clearly intent on avoiding a debate regarding specific historical accuracy, Laverty's screenplay features fictional characters, although there is a glimpse of Michael Collins in a cinema newsreel reporting the signing of Treaty and the establishment of the Free State.

The film's preoccupation is with the background to those events, the divisions they caused and the confusion that followed, and implicitly, their reverberations over the next 80 years of Irish history. The dramatic prism is the relationship between two brothers from a well-to-do family. Teddy (Padraic Delaney) is committed to the republican cause. Damien (Cillian Murphy) is a recently qualified medical student about to emigrate and work in London when he becomes politicised by events.

Loach orchestrates the drama with characteristically unshowy skill and compelling emotional involvement in a film featuring outstanding production values - Eimer Ni Mhaoldomhnaigh's handsome, authentic costumes, Fergus Clegg's detailed production design, and Barry Ackroyd's dexterous camerawork - that belie its low budget.

In the pivotal role of Damien, Murphy is masterfully subtle and effective, even in the contrived romantic subplot, which serves a purpose but feels dispensable. As his brother, assured newcomer Delaney is inspired casting, and it is a pleasure to see Liam Cunningham back in a substantial cinema role, as a Dublin trade unionist whose avid socialism was inspired by seeing James Connolly "set the place alight" during the 1913 Lockout.

In the movie's most harrowing sequences, one of the two brothers is subjected to horrific torture in which his fingernails are forcibly removed, and the other takes on the duty of executing a young friend who was naive enough to be an informer. It is the execution that is the more wrenching scene, and the one that prefigures the hard consequences of conflict to follow, as violence begets violence begets violence.