Ken Loach is a national treasure, it just seems that the national that produced him is not always keen to treasure him. With his second film on Ireland, The Wind that Shakes the Barley, taking the Palme D'Or at Cannes, he tells Donald Clarke why he keeps pricking the British conscience.

WHILE making his way to Dublin's Clarence Hotel for our interview, Ken Loach is stopped by a passer-by and congratulated on his recent triumph at the Cannes Film Festival. For the past four decades, Loach, who turns 70 this month, has been vying with Mike Leigh for the title of most admired British director of his generation. Yet, until now, he has managed to progress down most streets without being accosted by fans. Way back in 1966, Loach's Cathy Come Home, made for the BBC's Wednesday Play slot, managed to spur the British government into acting on homelessness. Three years later, Kes, the tale of a deprived youth and his love for a bird of prey, was immediately hailed as a classic. But, hitherto, you would never really have called Ken a celebrity. The coverage accorded the awarding of the Cannes Palme d'Or to Loach's powerful The Wind That Shakes the Barley seems, temporarily at least, to have changed all that.

Considering the film's subject matter - courage and compromise among those who fought in the Irish War of Independence and, later, the Civil War - we should, perhaps, not be surprised that the plain people of our nation have taken note of Ken's success.

"The most important audience is here," he says. "And particularly 'round where we made the film in Cork. They seem to think that it is true to the facts. And if the people who know most about it think it's okay, then it really is okay."

Not everybody is happy, however. Loach, an unreconstructed working-class socialist of the old school, has always got up the noses of right-wing blowhards in leather armchairs. If he thought that The Wind That Shakes the Barley, which stars Cillian Murphy and Padraic Delaney as two brothers divided by the Civil War, would, by virtue of its solid grounding in history, be granted an easy ride, he has been proved dead wrong. The most vitriolic response came from Simon Heffer, biographer of Enoch Powell, in the reliably fulminatory Daily Telegraph.

"Talking of hypocrisy, has there been any more nauseating lately than that of the bigoted Marxist film director Ken Loach on winning the Palme d'Or at Cannes," Heffer puffed, before going on to suggest, somewhat mysteriously, that socialists shouldn't allow themselves to stand anywhere near Emmanuelle Béart. "He hates this country, yet leeches off it, using public funds to make his repulsive films. And no, I haven't seen it, any more than I need to read Mein Kampf to know what a louse Hitler was."

Loach, a softly spoken man with a gentle temperament, almost loses his cool when I read out the quote. He mutters the word "disgusting" before allowing himself a resigned smile.

"He just sounds like a caricature of a right-wing extremist, jumping up and down. Actually it is sad for him, because he just makes himself look ridiculous. You just don't have these sort of conversations outside Britain. Nobody raises these issues in Italy or Spain. You won't find a historian who will challenge anything in the film."

It is true that the Black and Tans, the paramilitary reserves who visited such misery on the country in the 1920s, have found few defenders among serious historians. But Heffer, if he ever gets to see the film, might reasonably ask why the Crown forces are shown to be quite so unremittingly ghastly. Milton allowed even Satan some moments of considered reflection.

"The film is told from the point of view of those fighting for independence," Loach says. "And this is how those people would see the British. But the Tans and the Auxiliaries had fought in the trenches, and one of them does say: 'What do you expect? We were up to our knees in vomit and blood?' They, too, have been brutalised."

So what about Heffer's description of Loach as a Marxist? In the past Ken has dallied with such organisations as the Workers' Revolutionary Party. He made a party political broadcast for the Socialist Labour Party. He stood unsuccessfully in the European elections for George Galloway's Respect Party. It doesn't seem too unreasonable for Heffer to wave the M-word at him.

"I don't think he knows what the word means," Loach says with a sly smile.

Well, okay. If somebody who did know what the word meant called him a Marxist, would he accept it as a fair description? "I think it is very difficult to understand how the world works without paying attention to what Marx wrote," he says. "But hanging these labels on people doesn't help. When talking amongst friends you may describe yourself differently, but having a label hung upon you by a neo-fascist is not helpful. People who don't know the word's implication then just see it as something they have been taught to mistrust." Canny. Cautious. Still, nobody watching The Wind That Shakes the Barley could doubt that it is anything other than the work of men of the left. Screenwriter Paul Laverty, who also worked on earlier Loach films such as My Name is Joe and Sweet Sixteen, focuses on what he sees as the betrayal of the revolution's socialist ideals. A key scene finds a faction in an IRA flying column - later to join the Free State forces in the Civil War - siding with a landlord against his impoverished tenant.

"In the election of 1918 the Irish people voted for a programme which suggested a way of structuring the economy whereby land was held in common and the economic heights were held in common," Loach says. "That seems, to me, to be a very sensible way of ordering things. The balance of forces meant those ideas were lost, though they were paid lip-service to. The gombeen men won."

At one point a ruthless Anglo-Irish landowner, played with demonic glee by Roger Allam, suggests that a future independent Ireland may end up as a "priest-ridden backwater". This sounds like a phrase Bob Geldof might have used about the country back in 1979. Moreover, given Laverty and Loach's cynicism about what followed the Civil War, one might well infer they are allowing their villain a moment of savage prescience.

"Well, absolutely," he says. "Though you are in a better position to say than I. There is something in that. You always try to give your characters a moment of truth."

Loach's quiet anger has been a constant colour in his work. But he was not raised as a socialist. Ken has speculated that his dad, a factory foreman from the English midlands, whom he greatly admired, probably voted Tory. Jack Loach always wanted his son to enjoy the educational advantages he himself had been denied, so he was delighted when Ken won a scholarship to Oxford and appalled when, after graduating with a third, the lad announced he was going to become an actor.

"He was very sad," Loach agrees. "He had to leave school very early and he was a very bright man. So when I went to Oxford to study law that was a major boon. But he did live long enough to see a film of mine make it into the cinema."

After a period stomping the boards -including a spell understudying Lance Percival in a West End revue - Loach stumbled towards the BBC. The work he and contemporaries such as Alan Bennett, Trevor Griffiths and Dennis Potter did for The Wednesday Play counted among the corporation's greatest achievements of the era. "It was a massive stroke of luck to be among people who had such imagination and who were so forward looking," he agrees.

Interestingly, as early as 1965, when his adaptation of Nell Dunn's book Up the Junction got Mary Whitehouse into one of her trademark tizzies, the characteristic Loach traits were already in place: interest in working-class stories; unfussy camera work and, most significantly, a style of acting which makes scripted dialogue sound eerily natural.

"It's just a technique," he says glibly when I ask how it is done. "It's about encouraging actors to feel the words. The writing has to be very good." But, whoever writes for him, his actors still seem to exhibit the same persuasively realistic possession of their lines. What's going on? He begins squirming in the way a magician might if asked to explain one of his tricks.

"The thing is it should be like good music. You hear a great Chopin nocturne and you feel the pianist has just sat down and made it up as he goes along. The actors must feel these are their words. Often at the end of the process they will think they have improvised it, but they haven't really."

Such is his reputation that he has been transformed into an adjective. Any British film-maker working towards naturalism is likely to be described as Loachian. "I think that is only used by people writing about film because they feel they have to categorise. It neither delights nor enrages me."

Loach's first film to receive a theatrical release, Poor Cow, was a modest success. But Kes, based on Barry Hines's novel A Kestrel for a Knave, was a revelation. The film is now regularly sandwiched between The Third Man and Brief Encounter in critics' lists of the five best British films of all time.

"I think it is down to Barry Hines's great central image of a boy trapped on the earth with limited prospects and a bird who can soar in the air. We know he will never be that bird. That is always implicit; it is never stated. And, thankfully, we found people who could make it work."

Sadly, after the success of Kes, it looked, for some years, as if Ken might be lost to the cinema. When the British movie industry collapsed in the 1970s, Loach, whose talents were not suited to Confessions movies or adaptations of On the Buses, was forced to return to television. In 1971 he suffered a terrible personal tragedy when his young son was killed and his wife, Lesley, was seriously injured in a car crash.

Somehow the mini-boom in the 1980s that followed the founding of FilmFour and the rise of producer David Puttnam passed Loach by. He toiled away at political documentaries, most of which, he ruefully explains, were banned outright or screened in the wee hours of the morning.

"I couldn't have got work doing the weather forecast," he says, sadly. "They would all have said: oh, he is too biased. Then David Puttnam came to me and suggested I should do something on the Stalker Report into shoot-to-kill in Northern Ireland. And that became Hidden Agenda. That won a prize at Cannes and it all started up again."

Since Hidden Agenda's success in 1990, Loach has had a near unbroken run of critical triumphs. Most of his work - in films such as Riff Raff, My Name is Joe and Raining Stones - has demonstrated the director's continued interest in intimate social realism. Meanwhile, with The Wind That Shakes the Barley and the Spanish civil war drama Land and Freedom, he has widened his canvas somewhat.

This year's win at Cannes properly confirms Ken Loach as one of world cinema's most treasured ornaments. His acceptance speech, though delivered in his characteristically tranquil tone, demonstrated that he shows little sign of giving in to complacency.

"Our film is about a little step, a very little step, in the British confronting their imperialist history," he told the assembled masses.

Later, to the surprise of nobody, he compared the events depicted in The Wind That Shakes the Barley to the current US occupation of Iraq.

Fair enough. But every film is about Iraq now. Mission: Impossible III and X-Men: The Last Stand both somehow contrived to refer to that conflict. People are soon going to get sick of these allegories. . . Aren't they? Ken Loach smiles patiently.

"Well then maybe they should do something about it. Then we will start making films about something else. Do something about it."

He says this forcefully, but, being Ken, not forcefully enough to warrant our appending an exclamation point to the quote.

The Wind That Shakes the Barley is released on June 23