Few movies have inspired quite such an outpouring of pre-launch bile as has Ken Loach’s The Wind That Shakes the Barley, which is finally released in UK cinemas today. Mr Loach has been admired by his global directorial peers for four decades, but that didn’t stop him being abused for many things: holding Marxist views, being virulently anti-British, rewriting history, making depressing films about poor people, living in a posh house in Highgate despite his socialist principles, using Lottery money to make his unpatriotic philippics and being rude about the British empire which gave him a Start in Life.

The Daily Mail called him “this Marxist propagandist”, The Times called his film a “poisonously anti-British corruption of the history of the war of Irish independence.” The Telegraph’s Simon Heffer didn’t bother seeing it, but denounced its maker’s oeuvre as “repulsive”. The Sun complained that “It portrays British soldiers as trigger-happy mercenaries hooked on torture, burning cottages for kicks … [while] at the same time, cold-blooded Republican butchers star as figures of heroic bravery”.

To my considerable surprise, I found myself being quoted in the latter newspaper as someone hostile to the film, because I’d written that its most brutal scenes amounted to “a recruiting campaign for the IRA”. As I thought I’d made clear in the piece, I was entirely in favour of Loach’s treatment – propagandist agenda and all – because it made sense at last of the unspoken hatreds and desire for vengeance that seethed in the heads of the Irish generation.

Growing up in London in an Irish family during the IRA bombings was an uncomfortable time; it was enlightening to listen to my father and his friends as they tried to discuss Irish history and its long Republican shadows, without sounding like murdering terrorists. They were men and women whose parents had lived through this terrible time and had heard the stories that Loach’s film so vividly dramatises. But Loach, as far as I can see, doesn’t go far enough. He tries to be fair in suggesting the Black and Tans were a traumatised bunch of ex-Great War officers sent to keep the peace.

They weren’t. It was the Auxiliaries who were the former soldiers, sent to bolster the occupying army at £7 a week. The Black and Tans were drafted in to bolster the Royal Irish Constabulary, and they came from God knows where. They may not have been (as legend tells us) the dregs of Wormwood scrubs and Pentonville prison; more likely they were unemployed working-class men, physically robust, inarticulate and keen to have a crack at the Mick renegades. Their uniforms were rubbish (half army tan, half police black) and the pay only £4 a week, but they were told they could do whatever they pleased, killing included. The orders came from Lloyd George, filtered down to the likes of Colonel Smyth, the (English) divisional police commissioner of southern Ireland, who told his force, “Suspicious-looking people are to be shot on sight. No policeman will get into trouble for making a mistake.” Many policemen resigned, rather than open fire on their countrymen; their places were taken by more of the English visitors.

So the first European terror group to be sanctioned by a government was sent from England to put the fear of God into the Irish. They set fire to the centre of Cork and burnt the Town Hall, and next day wore burnt corks in their caps. They systematically trashed and burned towns in Galway and Clare. From a railway bridge outside Croke Park – Ireland’s Wembley Stadium – the Black and Tans machine-gunned a football crowd at random, killing 12 and wounding 70.

A letter to The Times in December 1920 ran: “Dear Sir, When the Germans were in occupation of Belgium, they destroyed private houses and murdered innocent people, giving the excuse that they ‘had been fired on by civilians’. The English armed forces in occupation in Ireland now destroy private houses and murder innocent people, in their turn giving the excuse that they have been fired upon by civilians. The English ministers who thus denounced Germany are silent. Yours, W B Yeats.”

Loach’s film is a harrowing look at the birth of a new independent nation, and the terrible sacrifices that were required by its founders. It doesn’t glorify shooting your enemies or your own people; it’s fully conscious of the tragic ironies attendant on taking sides and applying laws. If Mr Loach is guilty of portraying the consequences of a terrible initiative by the British, thereby embarrassing the patriotic and the reactionary, he deserves our praise. They should know better than to attack the messenger for bringing the bloody truth to British eyes, 80 years on.