FEW songs are more openly romantic than the ninth track on disc two of the latest Waterboys album, whose chorus requests: “Rukadenashiko, will you be mine?” Particularly when we know that the Japanese feminist sculptor and manga artist being asked that question is married to Waterboys frontman, the legendary Scottish singer-songwriter Mike Scott.

In fact Rukadenashiko, whose real name is Megumi Igarashi and whose pseudonym means “bastard” or “reprobate”, hadn't yet met Scott when he wrote the song, which includes the line, “the way that your smile outshines the sunshine”.

It was in 2015 that Scott, who to all intents and purposes is The Waterboys, first became aware of Igarashi. She'd been arrested for violating Japanese obscenity laws by creating a yellow kayak sculpture in the shape of her vulva and distributing 3D-scanner data of her genitals by email, and the trial made global news. Scott, who was in America at the time, heard about it on US TV programme The Daily Show.

“I thought her art was very clever," he recalls. "She made personified versions of the vagina in a very cute, funny way. I thought, ‘What she’s doing is fantastic and she’s funny.’ Even though she’d been put in jail by the Japanese police she was always smiling. I thought, ‘Wow, what a personality!’”

In keeping with the manner in which some digital-age friendships start, Scott began following Igarashi on Twitter. She followed him back. He later sent her a private direct message. “I DMed her,” he recalls, “as they say, and just told her how much I admired her and I said I liked her as a woman too and would she have dinner with me.”

Igarashi replied that it was too early to talk about romance, since they had never met, but, yes, when next he came to Japan it would be great to have dinner as friends. “So that was what we did. Very smart reply from her. Spared us the torment of one of these internet-only relationships.”

Scott’s music has long followed an ever-metamorphosing journey, transforming repeatedly throughout his career, and with an ever-changing band line-up the band's line-up. Each album brings some new twist or reinvention, in a path that has taken him from early success with single The Big Music through the stunning traditional music record Fisherman's Blues, an album of Yeats songs, to collections influenced by bluegrass and Nashville. The screenwriter Richard Curtis once described him as “one of the greatest pop stars who had ever lived” and his best-known single, The Whole Of The Moon as “one of the greatest pop songs ever written”.

Given all these twists, the surprise is that Scott continues to surprise. The earlier tracks on the new record, Out Of All This Blue, seem like a natural evolution from Modern Blues, his acclaimed 2015 album. It’s bluesy, American, with a new hip-hop twist. But the last five tracks, all inspired by Rokudenashiko, bring a shocking jolt of the new. This is music lit up by her smile, by pop sounds and Japanese culture, songs that thrum with the silliness and seriousness of love. So startling is the change that it almost feels as if Scott has found the Yoko Ono to his John Lennon.

Scott, 58, wrote his propositioning song Rokudenashiko in December 2015. “It was,” he says, “just before we met but after I’d begun to fall in love with her from afar.” The ridiculousness of his intentions, is encapsulated in the lyric: “When I told them my plan – they said, ‘Well is that so? But she’s in Japan.’” Not long after they made contact, he recalls: “We met up just as friends for dinner [in Tokyo] and we had a wonderful evening together, great chemistry, and at the end of the evening I asked her if we could have a romantic date next time, so she said OK and two days later we met for a second date. Then on our third date I played her that song.”

What is most striking is Scott's admiration for Igarashi's courage. “There was a moment in her case,” he says, “when she was arrested. The police came to her house at 6am and handcuffed her and put her in a car, and there were lots of photographers and the policewoman said, 'Drop your head'. Customarily when Japanese criminals are caught and photographed they bow their heads in shame, and she refused to bow her head, and there are photographs of her being arrested with her head held high.”

Igarashi was found guilty of distributing 3D data and fined £2900. The pair married last October and now live in Dublin together with their seven-month-old baby son, and Scott describes this as “a really good time in my life, a very adventurous and thrilling period”. The couple plan to go back to Japan twice a year, “to see Megumi’s family and friends and to take our baby”.

There are other reasons for Scott’s buoyant mood. One is his relationship with his daughter, Lila-Elodie, born four years ago to his then-girlfriend, the French-Irish singer Camille O’Sullivan (now involved with Game Of Thrones star Aidan Gillen).

“Many of the songs on this album came shortly after I became a dad, and I’ve got a little daughter, and that’s an endlessly unfolding fun adventure with her. I’m making up songs for my daughter all the time. It’s not so much that those then become Waterboys songs, because they’re silly songs, lyrics like, ‘Your right foot into the right shoe, and your left foot into the left shoe.’ But it does mean that my engines are running, my creative juices are on. It’s only a short hop from writing 'put your left foot in your left shoe' to a pop song.”

Scott describes himself as a “hands-on dad” to his children, who both live in Dublin. “I’m in baby overdrive. It's hard work, and it is blissful and he’s a wonderful little chap, very happy baby, but, boy, is it hard work.”

How does he juggle things? “Hands-on dad and hands-on band leader at the same time. As long as I don’t get things mixed up and start teaching him songs and changing the band members’ nappies, things will be OK.”

Scott has spent much of his life on a quest to understand big fundamental questions. In 2002, he and his then-wife Janette went to live in the Findhorn spiritual community. Today, he says: “Family life is a very demanding and rewarding spiritual path as billions have discovered before me. It took me a long time to realise this. I was a first-time dad at the age of 54. I really wanted to have children, so I’m very happy."

Born in Edinburgh, where he lived until his teens, Scott returned to the city aged 18 to study English and philosophy. This summer, he was back in Edinburgh for the festival. It’s a regular feature of his year that he goes there to visit his daughter, who accompanies her mother, O’Sullivan, on a month-long stint at the Fringe.

“It still feels very much like my home town,” he says, “I was on George IV bridge a lot on this trip because we were staying on the Royal Mile and I realised how many things have happened to me in my life, on or around George IV bridge. My first gig, for instance, of my first band was on Chambers Street.”

Scott still returns to Scotland frequently to visit his mother, a former university lecturer, in Largs, but he sees himself as rooted in Dublin for now. Nevertheless, he makes no bones about the way he feels about the fact he wasn’t able to vote in the Scottish independence referendum. “I would have liked a Yes vote on independence and a No vote on Brexit,” he says, “But I didn’t get a vote. If I’d come from Alpha Centauri three months before and lived in Galashiels for that time I would have had a vote. But though I’m born in Scotland, educated in Scotland, still a taxpayer in Scotland, still a property-owner in Scotland, because I hadn’t lived in Scotland for the past three months I didn’t have a vote. I think that’s shocking.”

He quips: “How could Scotland make that discussion without me and Irvine Welsh?”

Scott has spoken in the past about how his father left the family when he was just eight years old, and remained in his life only until he was 12 – Christmas 1970 being the last time they met during his childhood. When Scott was in his 30s, he tracked his father down to Birmingham and knocked on his door, demanding that he be in his life whether he liked it or not.

They remained friendly, and then six months ago, his father died of a “confluence of ailments". “I was glad to have some years with him,” Scott says now. “And we had a wonderful FaceTime on his birthday, which was four days before he died. We didn’t know that he was going to die, and he was on great form in his house. We had a lovely half-hour conversation so I’m very glad that happened. We also spoke on the phone just before he died.”

For Scott, these past few years have been among his most productive ever. There have been years, he observes, when he has not written a single song. “The last while," he says, "since 2014 or 2015, I’ve been writing a lot. At one point, in the summer of 2015, I was writing a song a day, which I hadn’t done since I was a teenager.”

Whether writing songs or not, Scott has always had music in his head. His autobiography, Adventures Of A Waterboy, begins with a description of him drumming on the floor of a bus, tapping out the beat of the music inside his head, only to be silenced by an angry bus driver. What surprised him most then was not the driver's fury, but that this person didn’t also hear inside his own head, the music that, for Scott, was always there.

Does the music ever stop? I ask. “No, it’s a constant presence. The music in my head just keeps going regardless of what’s going on in my life.”

His love of pop music comes across in the new album. It was, he says, what he grew up with in the 1960s, buying a pop record every week. “I love black soul music, Motown, Stax, Sly Stone, Isaac Hayes. And they were all making pop music, they were making three-minute songs that had hooks and funky grooves, and I love that."

It’s long been Scott’s view that the era in which he came to fame, the 1980s, was the death of music and a time when we lost our way politically. What does he think of the current climate? “We are in a time when both forces seem to be very active. I’d see one as an evolutionary force moving forward, a progressive force that prevailed in the 1960s and it’s still there in information technology and the way we’re more of a global community, but at the same time we’ve got this thing that was legitimised in the 1980s of greed and business monopolies and corruption. There’s a very difficult dance going on between them."

Nevertheless, Scott is optimistic. “I agree with Barack Obama and Martin Luther King that the arc of history is long and bends towards justice. Though shorter-term I’m not optimistic. I think Trump somehow will fall, be impeached, prosecuted, resign, or be voted out, and it will not be pretty.”

If there’s one feeling that comes across in the final tracks of Out Of All This Blue, it’s a buzz of optimism – not necessarily political, but personal. The album hums with the thrill of discovery, the excitement of coming to a whole new culture, the way it makes the world look entirely different.

The track, Payo Payo Chin, revolves around a Japanese expression for "good morning", and conveys the thrill of looking at the world through new words, and a new love. It’s like a waking up afresh to life.

Scott and his wife now mostly speak in English, but while they were courting, he took Japanese lessons. “Japanese of course has no root in Latin or any European language," he says. "It’s more difficult because of that, but also more fascinating. It doesn’t have tense. When I’m talking with Megumi she’ll say something and I can’t tell whether it’s happening now or if it’s happening in the future. She’ll just say I walk to post office, and I’m thinking do you mean you’re going to, or you did? There’s constant delicious confusion in our conversation.”

One misunderstandings that occurred between them was over their wedding, which took place in the Setagaya neighbourhood of Tokyo. “Because of the language problems,” he recalls, “Megumi told me it was Setagaya post office. And for the first six months of my marriage I thought I got married in a post office, then one day in our conversation it became evident that it wasn’t a post office, it was a ward [municipal] office. I was very disappointed.”

One song on the album, Yamaben, was written for Igarashi’s lawyer, Takashi Yamaguchi, who was her lawyer during the obscenity trial. “Megumi loves all the people that represent her, and she wanted me to write a song for Yamaben [the lawyer's nickname] and I think she thought she was going to get a 40-second acoustic guitar and vocal recorded down a telephone line joke song. But I worked on it all night and it became Yamaben, this psychedelic pop single. And she loved it and it got sent to Yamaben and he sent me the most incredibly courteous, diplomatic email, asking me to change one word in the song – which I did. I was just struck by the elegant courtesy of his email. Fantastic. Japanese courtesy."

Yamaben seems like nothing the Waterboys have created before. In the past, Scott has said it becomes harder with each album to leave the weight of past music behind – yet here he seems to have catapulted freely into new pop territory. “Gosh I’d forgotten I’d said that,” he says now. “I remember a time when I did feel that, but I don’t feel it any more.”

Why might that be? “Because,” he says, simply, “this record is a good one.”

Recently, he recalls, he listened back to his old albums in preparation for his upcoming tour. “And it’s been very interesting because the old albums have all got their charms, and some of them have more than others, but the new one’s got better melodies, better singing, better lyrics, better arrangements.

"I think it’s the best Waterboys ever.”

All Of This Blue is released on Friday (September 8) on BMG Records. The Waterboys tour the UK from October 18, including a gig in the Glasgow SEC Armadillo on Tuesday, October 24 (Tickets: 0844 844 0444 www.ticketmaster.co.uk/event/36005278A9E93FA8)

FULL TOUR DATES:

Wednesday 18th Bristol Colston Hall

Tickets: 0117 203 4040; www.colstonhall.org

Thursday 19th Birmingham Symphony Hall

Tickets: 0121 780 3333; 24 hr Hotline 0844 249 2222; BookingsDirect.com

Saturday 21st London Palladium

Tickets: 0844 412 4655; 24hr Hotline 0844 249 2222; BookingsDirect.com

Sunday 22nd Manchester Opera House

Tickets: 0844 871 3018; 4 hr Hotline 0844 249 2222; BookingsDirect.com

Monday 23rd Gateshead The Sage

Tickets: 0191 443 4661; 24hr Hotline 0844 249 2222; BookingsDirect.com

Tuesday 24th Glasgow SEC Armadillo

Tickets: 0844 844 0444; http://www.ticketmaster.co.uk/event/36005278A9E93FA8

Thursday 26th Dublin 3Arena

Tickets: 0818 7193000; http://www.ticketmaster.ie/venueartist/197033/888869