The Scottish composer James Dillon was a pretty punchy figure in the 1980s. “I used to say I was a musical terrorist, which didn’t endear me to many people,” he admits. “Especially as it was the time of the IRA and I had an Irish name. They thought who is this guy? What does he mean?”

Dillon is associated with the school of New Complexity, a loose term (loathed by its members) to describe six of the world’s most frighteningly, uncompromising modernists, all of whom had come to the fore in the 1980s and 1990s and whose music was among the most texturally dense, sonically extreme and structurally complicated of any works in Western musical history.

Bafflement came even from learned colleagues. Graham McKenzie, the director of the Huddersfield Contemporary Music Festival, which gives the UK premiere of Dillon’s latest work, The Leuven Triptych, on November 22, remembers being perplexed by his music when someone first gave him a CD. “There was this figure on the cover who looked like Robert Plant from Led Zeppelin,” McKenzie says. “Then I put the music on and thought, what is this? It was like some strange in-joke that no one had told me about.”

For many, Dillon’s wild aural rides, visceral and meticulously composed, proved him to be one of the most versatile British composers of his generation. Awards from the Royal Philharmonic Society and from the Darmstadt School in Germany (where he taught for a decade) attest to this.

Yet his music has fallen foul of the changing musical winds in the UK. When any of his works are performed here it’s virtually as samizdat. “The BBC is the only place that has been consistent [in supporting] me,” he says, “All the other establishment institutions have not been interested.”

It has forced Dillon (like most in New Complexity) to live, compose and gain commissions abroad for the past two decades, which he does with great success. The Leuven Triptych received its world premiere in Belgium, for example. I’m taking the train to London with Dillon from this concert. It feels a little like travelling with Lenin to tsarist St Petersburg. The new piece is a 50-minute, multilayered, dreamy mass of music that Dillon says he doesn’t necessarily “want the ear to follow”.

Why does he think he’s been given the elbow by the British establishment, I ask? “I don’t know if my personality helps,” he admits, “I can come across as a bit intolerant.” The accusation that is often levelled at Dillon, however, is that he and his fellow New Complexity practitioners are deliberately trying to make things difficult for audiences and performers. True? “Hmm,” he pauses. “I am looking for an endless intensity, [whereby] you rarefy the musical space so much that it does involve a certain type of complexity of learning. But there’s a heavy price to pay for that. That is: you’re not going to get so many performances.

“There’s a very famous composer, conductor, same generation as me,” he continues, “who, like a mantra, every time I bumped into him in Kilburn High Road, would say, ‘Oh, James, when are you going to write something we can do in two rehearsals.’ Why would I want to? I’m not desperate for performances. I’m engaged in the projects. It means you make sacrifices. I’ve always been sustained by being outside Britain.”

His first classical points of references were foreign: Webern, Stravinsky and Varèse, whom he had discovered when he was 19 from the back cover of a Frank Zappa album. It was the late 1960s. He was in a rock band, living in Cornwall, hanging out on the beach, doing pub gigs, taking a lot of drugs. “It was a way, way-out scene down there, very acidy, heading into oblivion. I was acting like I was going to kill myself.”

After a year at art school in Glasgow, drunk, in folk clubs, he decided to straighten out. He moved to London and embarked on a journey of self-education. He discovered Boulez at the Roundhouse, began private tuition in Indian music and tabla playing, studied Johann Fux’s 1715 treatise on counterpoint, Gradus ad Parnassum, and, in 1976, had his first composition, the fantastically satisfying piano work Dillug-Kefitsah, performed at Huddersfield.

The complexity came about as a way of creating music that approximates to the complexity of being alive today, he says. Which is why he was never tempted by minimalism. “I’m not keen on hypnotics,” he explains. “It’s why I gave up acid. They render you mindless; you stop thinking. There’s something politically and ideologically dangerous about it.”

But isn’t there a middle way? Composers who are producing more accessible music, such as Judith Weir and Julian Anderson, are the ones winning friends, aren’t they? “These are people who are — how does one put it? — embraced by the establishment. But are they winning audiences in France, Germany, Italy and Spain?” he asks. “The world is not England for me.”

Music by James Dillon is performed at the Huddersfield Contemporary Music Festival (www.hcmf.co.uk; 01484 430528) on Nov 21, 22 , 26 and 28

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