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After six days in Glasgow, Chris Thile has mastered his angry Scotsman impersonation. It sounds like Billy Connolly, but – unless Connolly was responsible for the inebriated heckle at last night’s Punch Brothers show – Thile is actually channelling the indignation of an unspecified purist: “Oh, play some bluegrass, fi’ Christ’s sake!” Stopping only to swallow a chunk of his Starbucks Very Berry scone, Thile continues, “It was another ‘Judas’ moment to add to the collection.”

From the moment the mandolin-wielding golden boy of 21st-century bluegrass disbanded Nickel Creek, citing the need to experiment, the heckling was inevitable. Thile says he always knew that the tastes of folk fans in the States were entrenched. But since his three-year-old outfit Punch Brothers arrived to play a series of shows at the Celtic Connections festival, he adds: “I didn’t realise the bluegrass police had moved over here too.”

It takes only a cursory listen to Punch Brothers’ new album, Punch, to guess why a section of fans may have been startled. Few musicians – well, none – have intertwined bluegrass instrumentation and spontaneity in the strictures of modern classical. The Blind Leaving the Blind – the four-movement lion’s share of Punch – is by no means easy listening. But as a portrait of an artist defining his musical territory in the same way that, say, Joanna Newsom did with Ys, it is remarkable. Elvis Costello’s North also springs to mind.

Crisis informed its creation: the collapse of his marriage after just 18 months, then the collapse of the Christian beliefs that Thile’s parents had instilled in him throughout his young life. Now a tousled, unshaven 27, Thile says, “It took me a long time to realise that the world doesn’t necessarily have your best interests at heart.”

Before all of that though, he says that the first thing he lost his faith in was commercial success. On the back of two million sales for Nickel Creek’s 2002 album This Side, even the Albert Hall was sold out for them here. “There was a definite pressure to keep the numbers [of albums sold] going. And the reason I had to get out of it was that I didn’t care any more.”

Well, he had certainly been doing it long enough. Growing up in California, Thile picked up a mandolin aged 5. Three years later, he was entering adult competitions – and winning them. At 15, the constant demand for his playing necessitated a family move to Nashville. Thile says that his father did his best to simulate an atmosphere of normality. You suspect that, for Scott Thile, playing alongside his son in Nickel Creek was a way of maintaining that normality. “The religion of my youth was fear-based,” the younger Thile says, with no hint of animosity, “and I think a lot of religion is. It’s left me with an overall fear of death, which I kind of resent. I feel that’s no way to really live.”

At 23, he was young to marry and yet pretty old not to have asked himself many of the big questions that usually come with adolescence. “Well, I had the mandolin to keep me company,” Thile says. “I didn’t need to rebel as long as I had this instrument to pick up and practise.” Perhaps being in a group with his dad conspired to put the brakes on the self-discovery.

By the time 2005’s Why Should The Fire Die? appeared, Thile’s lyrics suggested that, beneath the burnished roots-pop exterior, an impasse had set in. “What will be left when I’ve drawn my last breath . . . Will I discover a soul-saving love/ Or just the dirt below me?” The lyrical shift didn’t go unnoticed by his parents. Years later, he says he is only just beginning to have “some good religious conversations” with them: “They’ve even called me up and said, ‘Hey, remember when you were little, how we didn’t let you do this or that? Well, we’re sorry. You wanna talk about it?’ ” Having also joined us, Punch Brothers’ bassist Greg Garrison recalls being aware of Thile well before he met him. “Everyone was aware of Chris’s musical prowess, but also aware of the fact that he was very Christian. And in that sense, we were wanting him to break that mould,” he says.

Thile had unknowingly sown the seeds of just such a transition. He now says that the fall-out from his marriage (to a Nashville clothes store assistant) was “the best and worst thing that happened to me”. Thile found a sympathetic ear in fellow country prodigy Gabe Witcher. It happened that Witcher – whom Thile had known since childhood – had also been through a painful break-up.

Punch Brothers emerged, as Thile put it, after the two “got together one night just to drop a ton of money, drink too much wine, eat steaks and commiserate about our failed relationships.”

Credited to Thile but featuring his fellow Punch Brothers, 2006’s How To Grow a Woman combined originals with assorted covers, some country, some less so. Sadly the stunning eight-minute version of Radiohead’s Morning Bell that features in the group’s live set didn’t make it on. One song that did, however, was their version of the Strokes’ Heart In a Cage, complete with swear-word. Fan forums reached boiling point over his use of “f***” – no matter that he didn’t write the words. “Yup,” one fan wrote, “Chris managed to sneak-attack an F-bomb into his new album. Ugh . . . Why? What does it prove? I hope that Chris loves people losing respect for him. ’Cause I just lost a bunch of it.”

I tell Thile and Garrison that the virulence of the objections took me aback slightly . Even if we are only talking about Nickel Creek’s more reactionary fan-base, I thought rednecks swore. “They do!” Thile hoots. “All the time.” “They just don’t want their kids to hear it,” Garrison says. Thile adds: “They don’t want to have to put any effort into the entertainment of their kids. In the States, parents have decided it’s the entertainment industry’s job to raise their kids – that Nickelodeon should be doing it. One thing I can say about my parents is that they put the hours into it.”

None of this, I say, is going to pan out very well for the two million Nickel Creek fans in America who are hoping this is just a phase Thile is going through. “Well, you can’t please everyone,” Garrison says, “but we need to take a look at how we can best present this music to certain audiences so as to have our cake and eat it. Do you know what I mean?”

Well, I suggest, if you’re not going to eat your cake, I say, what else can you do with it?

Next to Garrison, the former future of bluegrass nods thoughtfully, before a now-familiar heckle resurfaces in his mind. “What else can you do with a cake? You can shove them in people’s faces. Hahahah!”

— Punch is released by Nonesuch on Feb 26

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