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Nutini’s new album, Caustic Love, releases this week Image Credit: Supplied

Having first tasted success in his teens, Paolo Nutini became one of Britain’s biggest solo stars when his second album, Sunny Side Up, sold two million and topped the charts three times.

Nutini had originally been bracketed alongside such pretty-boy singer- songwriters as James Blunt and James Morrison, but Sunny Side Up singled him out as a talent of real depth and staying power.

Instead of bringing happiness, though, his growing fame left the young Glaswegian feeling disorientated. His father Alfredo and grandfather Giovanni had both worked long hours in the family’s fish-and-chip shop, The Castelvecchi in Paisley, and it had been thought that Paolo would follow in their footsteps.

Struggling to stay in touch with his unpretentious roots, he took a long break. With a split from childhood sweetheart Teri Brogan still fresh, he flew to the family’s ancestral home in Tuscany with his guitar and ended up staying two months.

On his return, he disappeared from view. It wasn’t a celebrity meltdown — Nutini is too grounded for that — but a deliberate retreat from the limelight. “I’ve been through a few growing pains,” he tells me. “Never mind growing up in public, I just had to grow up, full stop.

“I thought my life was going to pan out in a certain way, and it was turning out very differently. I had a lot of frank conversations with my family. It’s hard for me to talk about the specifics, but the way we chat to each other has changed completely.

“The end of a long-term relationship was another factor. I needed to step back, and take stock.”

Nutini, 27, hasn’t exactly been idle since his last major appearance, at an Olympics event in Hyde Park in 2012. That gig, he says, wasn’t his finest moment (though the thousands of fans I saw enjoying themselves might disagree).

“I was playing with Snow Patrol and Duran Duran, but my songs are not singalong epics like Chasing Cars or Rio. I felt like the black sheep.”

If such self-doubt is typical of Nutini, who is engaging company despite a tendency to ramble, his insecurities may shortly be banished for good. In the five years since Sunny Side Up, he has been writing for his third album, Caustic Love.

Out now, and on course to become the fastest-selling album of 2014 when it charts this Sunday, the record is his best yet, embracing a more modern sound and adding greater emotional grit.

Paolo’s voice retains its distinctive Celtic lilt, but his songs now lean more heavily on contemporary American styles, with the processed rhythms of hip-hop and RandB thrown into the mix alongside the acoustic textures and heartbreak ballads of old.

Among the highlights are gospel lament Better Man and the Marvin Gaye-like Diana, a moody piece that showcases Nutini’s soulful falsetto but might alienate the more pop-orientated sections of his audience. The singer also explores new terrain on Let Me Down Easy, which samples a Bettye LaVette hit, and the funky, electronic Fashion, which features a dazzling rap from Janelle Monae.

“Janelle is wildly entertaining,” Paolo enthuses. “She has real class, and can get her picture on the front of glossy magazines without having to behave like Miley Cyrus.”

The last act signed to Atlantic Records by the late Ahmet Ertegun, legendary label boss behind the success of Ray Charles, Otis Redding and Aretha Franklin, Nutini has come a long way since his 2006 debut album These Streets.

Back then, Ertegun hailed him as “the most promising artist we’ve had in years”. Now, with Caustic Love, Paolo is fully justifying his mentor’s faith — with a healthier perspective on fame.

“Some people say I’m lucky to have escaped the life that my dad had, working in a fish-and-chip shop, but I don’t see it like that. If I’d followed in his footsteps, I’d be running my own business. It wouldn’t have been like going down a mine!

“I’m still involved in the shop. The decor hasn’t changed since the Fifties, but I’m trying to move things forward without losing the charm. I can’t go in and start cooking fish suppers or deep-frying Mars Bars, but the shop is something I’m very proud of.

“I’m lucky to have had good male role models in my grandfather and my dad. My dad is a bright guy. He can look into the mirror above the fryer and be happy at the man staring back. A lot of the good in me, the honesty and romance, comes from him.’