A GALLIMAUFRY of words pours annually out of Scotland but of the multitude of writers shaping them, only two will regularly and consistently make headlines around the globe. One is JK Rowling. The other is screenwriter Paul Laverty, a Scot of Irish extraction who was born in Calcutta, raised in Wigtown, educated in seminaries in Glasgow, Aberdeen and Rome and who has ended up in Madrid by way of Nicaragua and Los Angeles.

I visit each of those places over the course of an engaging afternoon in Laverty's company but dwell longest in Nicaragua and Rome, the twin crucibles in which his worldview was formed - a worldview that has played a significant role in shaping the way Scotland is represented on film today.

The 49-year-old is too self-effacing to enjoy an introduction that compares him to the creator of Harry Potter but his success speaks for itself. In tandem with veteran director Ken Loach, Laverty has created some of the most controversial and critically acclaimed British films of the last decade.

Three of these - My Name Is Joe (1998), Sweet Sixteen (2002) and Ae Fond Kiss (2004) - were set entirely in Scotland and form the so-called Glasgow Triptych.

Another, Carla's Song (1996), was partially set here and helped consolidate Robert Carlyle's international standing postTrainspotting. In all, four of the six films Laverty has made with Loach have featured in competition at the Cannes Film Festival and three of them have won awards.

The most recent was The Wind That Shakes The Barley. It stars Cillian Murphy as a young doctor in 1920s Ireland who takes up arms against the Black and Tans in the Irish war of independence and is then sucked into the civil strife that follows. It won the prestigious Palme d'Or, the first time Loach has taken the top award at Cannes.

Laverty's is one of the most important and controversial voices in Scottish cinema, yet in a sense he stands apart from the native industry. When an open letter to Jack McConnell was published recently, calling for a rethink on the merging of Scottish Screen with the Scottish Arts Council, his name was not on the list of signatories.

Where, then, does he think he stands in the canon of Scottish film? And, given that he lives in Spain and works with an English director, does he view the scripts he writes as being about Scotland or simply set here?

We meet in the bar of the Glasgow Film Theatre, the day before Laverty is to host a special screening of The Wind That Shakes The Barley. Two days earlier he was in Cork;

by the weekend he'll be back in Madrid.

"I think it's important when you're writing a story to be culturally specific, " he says. "In every film I've done, whether it's Sweet Sixteen or My Name Is Joe, we've tried to make it truthful to where we've shot.Where you live marks you to the core so I think the films are very specific to Scotland. But if you get a story that's humane and three-dimensional, being specific is no handicap to being universal."

As for his place in the canon, he never thinks about it. "I can't write like that. You have to just follow your instinct and write with conviction."

That his instincts and convictions tend to chime with Loach's is obvious but beyond that his explanation of their working relationship is foggy. He finds it difficult to talk about his friend, he says. There is mention of their relationship being "organic", some talk of its "complex interplay".

"I can't write to order, " he adds finally. "I have to find material that fascinates me.

But then if I'm going to work with someone like Ken who has had a long career and tried many different things, I have to find something that's equally fascinating to him."

Ireland, he says, has long held an attraction for both of them.

The origins of their relationship lie in Nicaragua. Laverty first went to the small Central American country in 1984. He was in his mid-20s and working as a lawyer in Glasgow, but was keen for adventure and becoming increasingly fascinated by the Marxist Sandinista regime which had come to power in 1979 by overthrowing the old dictatorship, much to the chagrin of the US.

He returned in 1986 for a two-year stint with the National Commission for the Promotion and Protection of Human Rights.

His job was to record testimony from those who had been attacked by the Contras, the CIA-backed counter-revolutionaries.

He also spent time in El Salvador and Guatemala, an experience that changed the way he viewed almost everything.

"I met the most incredible range of people, from ex-CIA agents to Contras who had mutilated people, families who'd had their children kidnapped and murdered. I met plumbers from Germany coming to lend a hand, Buddhists meditating for peace, cynical right-wing journalists, left-wing idealogues. I saw the entire range of human experience. And I also I saw war. I'm sure that the experience of Nicaragua had a massive effect on me when I was writing The Wind That Shakes The Barley."

One effect was his determination not to romanticise violence. He tells a story about an illiterate young boy he once met who had fought with the Contras.

"He described how he'd finished off people who had been shot in an ambush.

What he did was cut them to pieces with a knife. It was amazing talking to this young kid. I could see that he was destroyed as well, that he was another victim. I'll never forget his face and his manner. I'd be very surprised if he was still alive today."

LAVERTY then returned to Glasgow and wrote a screenplay. It was called Carla's Song and it was about a Glaswegian bus driver who meets a Nicaraguan exile and travels with her to her homeland to face her past.

"If someone had told me I'd go into film I would have laughed. But I was tired of writing human rights reports, journalistic pieces, speaking to delegations. In my innocence I thought making a film would be a way of exploring it." What happened next he describes as "another accident".

"A friend got hold of Carla's Song, which had been written but not made, and sent it in to USC. They read it and awarded me a Fulbright Award."

USC is the University of Southern California; the Fulbright Award was for a year's placement at its School of Cinema and Television (alumni include George Lucas, Sam Peckinpah and John Carpenter). It was 1993, 12 months after the Los Angeles riots.

Laverty moved into a Latino area in downtown LA, and a house filled with illegal immigrants and "old white trash who were poor and racist and couldn't stand the fact they were living with these people from across the border". The area was infested with gangs; at night, gunshots rang out. "It was amazing. I could have written 100 screenplays there."

Instead he wrote just one, Bread And Roses, filmed in 2000 with future Oscarwinner Adrien Brody in a lead role. By this point Ken Loach had entered his life, agreeing to make Carla's Song but only after he had completed Land And Freedom, a film about the Spanish civil war. He invited Laverty to join him on set and offered him a cameo; more importantly he brought Laverty together with his future wife, Iciar Bollain, who had the main female role.

Today the couple live in Lavapies, Madrid's old Jewish quarter, with their sons, five-yearold Lucas and two-year-old Liam. "It's very lively and very noisy, " says Laverty. "When I stand at my window with my wee boy we can say goodnight to Africans, Bangladeshis, Gypsies, Moroccans, Chinese. It has a real sense of a city changing." He likes it, he says, because "I'm just one more stranger there".

INfact I can't help wondering if he's a stranger wherever he is. Wanderlust seems bred into him. Laverty's greatgrandfather came to Glasgow from County Donegal to work in the shipyards, and his mother is from County Limerick. Childhood holidays were spent on his uncle's farm in County Cork - the same farm in which IRA guns were hidden by his maternal grandfather during the war of independence.

Laverty was born in Calcutta in 1957. His parents moved there because they wanted "an adventure" but his father caught TB and the project was cut short. The family returned to Wigtown, in Dumfries and Galloway, where they ran a small business. Laverty lived in Wigtown until he was 12. "It was an idealistic childhood, " he says, "a wonderful experience because we had total and absolute freedom."

Then came seminary: two years in Langbank, four years at Blairs College in Aberdeen and two more years at the Pontifical Gregorian University in Rome. In the 450 years since it was founded it has produced 14 popes and 20 saints. Laverty, for his part, studied philosophy and learnt Italian. But critical thinking wasn't in the marrow of the place, which irked him. So too did the tendency to see things in black and white.

"I always distrust that in any walk of life.

You have to be aware that we are full of complexity and contradiction and that's really stuck with me - But I couldn't have written Ae Fond Kiss without that experience. Talking to young muslims and seeing how they felt the weight of Islam and the weight of previous generations I realised it was similar to my own experience with Catholicism. We realised we had more in common than not."

Would he have made a good priest?

"No, it would have been a ridiculous idea.

Seminary became increasingly claustrophobic as I got older and asked more questions and it became really intolerable towards the end, particularly in Rome."

Gone too is his grasp of Italian, supplanted by the Spanish he learned in Central America and which he uses daily in Madrid.

But one thing he has never lost is his questing spirit. Like the stories he writes and the films he makes, he is both Scottish and international in outlook. His vision and interests are expansive but he retains the ability to look in forensic detail at Scotland and the Scots; and perhaps, after all, it helps that he does it from a distance.

"I just want to know what is beyond my own experience, " he says simply. "I have an incredible curiosity for what's happening on the other side of the mountain."

And that journey continues. Another screenplay for Loach is finished, this time about east European immigrants finding their feet in Britain, and Laverty is currently working on a story set in 16th-century Spain.

I ask if it's Don Qioxote, recalling the curse that befalls anyone trying to film Cervantes's novel.

"No, " he laughs. "I promise it's not Don Quixote." Tilting at windmills just isn't his style.

The Wind That Shakes The Barley is out now