"I just ran away," John Cale says with dark, sad eyes. "But I felt guilty. That's the thing about traitors. I didn't think I'd really done my best for the place that I'd come from." It doesn't take the approach of St David's Day to get John Cale talking about Wales, Welshness and why he left it all behind. For the past 12 months, it's been the main focus of his thoughts.
In person, at the age of 67, the avant-garde composer, prolific producer and Velvet Underground legend resembles a Tim Burton vision of a veteran rock star, with an accent once described as "West Village/Welsh Village".
Cale's in London to perform his classic album Paris 1919 at the Royal Festival Hall on Friday, but he's preoccupied by matters closer to home. He was asked to represent Wales at last summer's Venice Biennale, and set to work on Dark Days, an "emotional and personal" 49-minute, five-screen multimedia piece about his relationship with his native land.
Although he resides in Los Angeles, Cale keeps a keen eye on Welsh affairs. He's full of praise for the former first minister Rhodri Morgan and the political progress made by the Welsh Assembly in "presenting a solemn face to Westminster", and considers himself a patriot rather than a nationalist ("The word nationalism is a scary concept, with far too deep a history of blind aggression"). He still has family and friends in the Amman Valley and visits Wales regularly, but Dark Days involved a particularly soul-searching homecoming.
With sound and pictures, Cale retraced his childhood. The most moving part was returning to the house in which he grew up, filming the dawn breaking and recording the ambient noises of the house settling and the hum of distant traffic.
"Looking out of what used to be my bedroom window, I realised how different it all was, so built-up. But certain things hadn't changed at all. I looked at the wallpaper on the ceiling, and thought 'I remember putting that up!'"
One topic Dark Days deals with is Cale's relationship with the Welsh language. He speaks his mother tongue "falteringly" now, but although he grew up the son of an English coal miner, for the first seven years of his life he spoke nothing else. "I couldn't talk to my father until I was seven. English was something I learned at school." Cale blames his grandmother, whom he describes as "ferocious", for driving him away.
"I did not like her at all, and she did not like me. She made it very plain. When my mum was taken ill and had a mastectomy, I remember my grandmother telling a neighbour who enquired how Margaret was: 'You know, she's never been right since she had him.' And I just wanted to yell out 'Hey, I haven't done anything!' It's stayed in my head."
New York wasn't Cale's first port of call. A member of the Welsh National Youth Orchestra, upon leaving grammar school in the early Sixties he won a music place at Goldsmiths College in London. He soon gained a scholarship to Tanglewood in Massachusetts to play viola with the Boston Symphony Orchestra, where he worked with John Cage. It was a recommendation from Cage in 1963 which took Cale to New York, where he joined the minimalist composer La Monte Young's Theatre of Eternal Music. With Young, Cale learned the "drone" technique, practising holding the same note for hours on end.
It was while in New York that he formed a close friendship with a young songwriter called Lou Reed. The pair shared everything: an apartment, dirty needles and the hepatitis virus. And they formed a band.
With Reed's friend, Sterling Morrison, and, later, Moe Tucker, the Warlocks became the Falling Spikes who in turn became the Velvet Underground. When VU came to the attention of Andy Warhol, who became their manager and patron, everything changed. The Velvets were appointed house band at Warhol's Factory collective, toured with the Exploding Plastic Inevitable show, and became darlings of the New York demi-monde.
Cale clicked with the clique instantly. "I'd been working for three hours a day holding a drone, and I'd go to the Factory and they had the same work ethic. Andy would be making films, and Gerard [Malanga] was on the floor making silkscreens. Work was fun and fun was work."
Warhol taught Cale that "the tools of art are anything you can put your hand on". And in the Velvet Underground, Cale, nominally the band's bassist, put his hands on assorted instruments to great effect. The iconic viola drone on "Venus in Furs" is his work, as is the distorted organ on the 17-minute "Sister Ray".
The Velvets recorded a little-bought but immeasurably influential debut album in collaboration with the German ice maiden Nico, one further album, and then began to disintegrate. "Lou fired Andy and didn't tell anyone about it," Cale recalls. "I was furious about that. Also, when we began, songwriting was a four-part collaboration without resentment over who wrote what part, and we all joined in on the copyright. We all went out to promote it, and we all got the benefits. There was an element of trust. But later that became an issue, and it was corrosive."
Cale was one of the first musicians of his generation to attempt the dark arts of the recording studio. After leaving the Velvet Underground in 1968, he produced Nico's harmonium-heavy second album The Marble Index, and then The Stooges, overseeing several immortal riff-laden classics, including "No Fun", "1969" and "I Wanna Be Your Dog".
Throughout the Seventies and Eighties, Cale's services as a producer were much sought-after. Making the Patti Smith Group's landmark 1975 debut Horses, Smith lost a stone and Cale lost his mind – he compared the experience to shadowboxing. A decade later, Cale was asked to produce the debut by Happy Mondays, an experience he describes as "a very quick nightmare. I had just stopped drinking. The band complained that I was on a health kick: all I did was sit around eating tangerines all day long. Bez and Shaun [Ryder] have this amazing ability to walk into a place and unravel whatever kind of cohesion had been going on beforehand."
He also hooked up with Nico, then living in Manchester and addicted to heroin, for one last album, Camera Obscura. It must have been tough seeing his friend and sometime lover in a state of decline. He sighs. "Everyone organises their life the way they can. She organised hers around a drug. There was always this moment [in the studio] when there would be tears. She'd go away, you'd do your adorning of the tracks, you'd play back the finished product, then there would be tears of happiness: 'Ohhh, eet ees beautiful!'"
Cale spent decades as a friend of narcotics. "You take drugs thinking 'Wow, I'm gonna get through a lot of work'. And I guess I did, but nothing like what I got through without them." There must have been a time, though, when he saw drugs as facilitating the creative process rather than hindering it. "Yeah, but it was a fantasy. I got my creative process done whatever, but it's the time that was wasted. Because you don't have an idea of how time passes when you're in that state.
Last year, Cale organised a travelling tribute to Nico, Along the Borderline, featuring an array of guest vocalists. "The point was that there's a rich seam of female singers out there who really love Nico for what she wrote and sang, and it's really untapped."
His other ongoing live project is to recreate his own debut album. Which may not seem a very John Cale thing to do. I ask whether he's ever wondered why, of his 30 solo albums, Paris 1919 has become singled out as the one to hear. "Maybe because it was genteel and kind of poised. It has mythical qualities. At the time I was at Warner Bros in 1972 in the middle of the Cold War, and I thought 'Where did all this begin?' Paris, 1919."
One of Cale's most-celebrated solo recordings is his 1991 version of Leonard Cohen's "Hallelujah". Cale is bemused at that song's unexpected afterlife as a showbiz standard.
More recently, he has also – brilliantly – covered LCD Soundsystem's "All My Friends" for a single release. I ask whether he's familiar with that band's song "Losing My Edge" in which the protagonist, like a muso version of the Devil in the Stones' "Sympathy", boasts of being present at every turning point in musical history.
He isn't, but I put it to Cale that it describes him pretty well. "I don't do funerals or weddings," he laughs, "but I've opened and closed a lot of clubs."
1942 Born in Garnant, South Wales. Cale does not learn English until he is seven.
1960 Studies musicology at Goldsmiths, London.
1963 Moves to New York where he meets Andy Warhol and Lou Reed.
1965 Moves in with Lou Reed and forms a band with Sterling Morrison and Angus MacLise, called the Warlocks. They later change their name to the Velvet Underground and play their first gig for $75 in New Jersey.
1967 Their first album, The Velvet Underground & Nico is released. Andy Warhol is a producer.
1968 Marries Betsey Johnson, a fashion designer, only to divorce less than a year later. Cale leaves Velvet Underground after Reed forces him out.
1970 Releases first solo album: Vintage Violence.
1973 Moves back to London and signs a contract with Island Records for six albums in three years.
1977 On stage in Croydon, decapitates a dead chicken with a meat cleaver. Two bandmates leave.
1983 His lawyer starts to sort out the VU's finances. After three years, the first royalty cheques arrive.
1985 Daughter Eden Myfanwy is born. Cale celebrates with a bottle of wine and a gramme of coke.
1990 Velvet Underground reunite at a gig in France.
1993 The reformed Velvet Underground tour Europe.
1996 VU inducted in to the Rock and Roll Hall of Fame.
2000 Gets honorary degree from Antwerp University.
2009 Represents Wales at the Venice Biennale.
John Cale & the Heritage Orchestra perform 'Paris 1919' at the Royal Festival Hall, London SE1 on Friday. Go to: southbankcentre.co.uk