I have embarrassed Robin Pecknold, the frontman with the Seattle four-piece Fleet Foxes. “Have I ever what?” he says. Has he ever used his music to make himself more attractive to a woman? He smiles to conceal his discomfort that I might even think him capable of such a thing. “No, no . . . I mean, I’m the wrong guy to ask that question. That’s the last thing I would ever do. In the big debate about what music is and how it evolved, some people reduce it to a mating call, but me, personally? I think music happens because our brains are too complicated to be still all the time, you know?”

Half an hour after coming off stage to a rapturous ovation at Brighton’s Audio club, Pecknold is too distracted to appreciate the irony of his utterances. Outside the venue, two young Japanese Fleet Foxes fans stare at him with an air of respectful adoration. If truth be told, it’s a reaction that isn’t restricted to the other sex. It’s hard to recall the last time a recorded noise elicited the sort of praise reserved for Fleet Foxes’ celestial four-part harmonies.

Then, because of a last-minute booking at the Festival Hall in London as support to Elbow, the band found themselves playing to a full house. “Hi, we’re U2,” joked Pecknold. “We’ve been in the UK for three weeks now. We started with an audience of 100, then 300, 600 and now we’re here. Wow, it’s like a compact career.”

“Next time you’ll find us at the 02,” chipped in the keyboardist and mandolin player, Casey Westcott.

“Yeah,” added the drummer Joshua Tillman. “In fact, we’ll probably just do one huge gig, you know, for the whole of Europe.”

Fleet Foxes do a nice line in modesty. The nearest they get to arrogance during their Brighton show comes when the freewheeling backwoods canter of Ragged Wood comes to an end and Tillman and the bassist Christian Wargo exchange high-fives.

Afterwards Pecknold points out that often Fleet Foxes are no less startled by their vocal chemistry — a comparison with Crosby, Stills, Nash and Young barely begins to do it justice — than the rest of us are. Only 12 months have elapsed since Pecknold wrote Quiet Houses, the song that prompted him to junk everything they had worked on and start again. What changed?

“Prior to that, there were a few songs we were working on that were very much focused on the lead vocal, you know?” He almost baulks at the apparent gaucheness of such a conceit. “And I wanted to do a song that was the extreme opposite of that — where the vocals were just part of the music, and not just a platform for this guy, you know?”

Not for Pecknold the ego-massaging benefits of lead-singerdom. Fleet Foxes’ . . . well, let’s call him their primary songwriter, finds himself getting embarrassed “very quickly” by the mildest of misunderstandings. He relates a story about a show in Oklahoma with the bucolic freak-folkers Blitzen Trapper in which the venue owner’s wife served up separate meals for both bands. Pecknold asked for vegan food, but when he returned to eat it, “some guy who looked like me had been given the food”.

Not a major faux pas, you would think, but Pecknold was so embarrassed that he had to run back and hide in the van. It’s a tendency, he says, that his girlfriend finds exasperating at times. “If I order a coffee and they give me the wrong one, I would rather throw it away and buy a new one,” he smiles. “It drives her nuts.”

If the tics and traits of an “inward-looking” childhood remain mostly intact, it’s perhaps not so surprising. “By the time I was dressing myself,” Pecknold says, “I was overweight to the point where I would want to wear a T-shirt in the water.”

When he was 14, though, he cut animal and dairy products from his diet and the pounds started to fall off. “I went on a big bicycle trip — like a summer camp thing — and decided I didn’t want to eat all the crappy food that everyone else had. At the same time, I had just heard about what a vegan was, so I told everyone that I was a vegan so I could eat special food.”

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