IN the hills behind Dunoon, an Oscar-winning actor and a 1980s pop star were walking through the forest, humming fragments of tunes and ideas for lyrics as they wandered in the Argyll wilderness.

The pair came to a house at the edge of the forest, and settled at the kitchen table where they quickly scribbled their thoughts down on paper.

Later that day, the 1980s pop star said his goodbyes to the Hollywood actor at her home, caught a tiny ferry across the Clyde from Dunoon to Gourock, and set his sights on the bright lights of the world's biggest stages.

Yet when Gary Clark first picked up a voicemail on his phone from 'Em Thomson' he thought it was, well, another Em Thompson.

"One of my best mates has a daughter called Emily Thompson," says Clark, beloved to fans of 1980s Scottish pop as the lead singer of Danny Wilson, speaking from his home in Broughty Ferry.

"So when I got a voicemail saying it was Em Thompson I called the number back thinking it was Emily, my pal's daughter. It was only as the phone was actually ringing that it dawned on me I was phoning Emma Thompson. When she answered, I had to quickly pretend that I'd intended to phone her. I took myself off-guard."

And so began Clark's songwriting relationship with the star of Harry Potter and Sense and Sensibility, as the pair made their first collaborative sketches towards a forthcoming stage production of 2005 movie Nanny MacPhee.

Gary Clark's journey from busking in Broughty Ferry to staging shows off-Broadway couldn't have been any more circuitous if he'd taken control of that Dunoon ferry and sailed it the long way round to New York.

He first came to prominence as the songwriter for Dundee band Danny Wilson scoring a solid-gold classic in the shape of their swooning late 80s pop hit Mary's Prayer.

At a time when Scottish pop was king in the UK charts, Danny Wilson's success was comparatively short lived, with one further hit, 1989's The Second Summer of Love, before they split in 1990, their sophisticated sound at odds with the rave culture and Madchester scene that song nodded at.

The band featured Kit Clark, Gary's brother, who went on to form Dundee indie outfit Swiss Family Orbison with Deacon Blue drummer Dougie Vipond, and Ged Grimes, who later joined Simple Minds.

Clark, 57, moved to Los Angeles with wife and manager Alison, and carved a successful niche as a songwriter and producer for other artists, including Natalie Imbriglia, Demi Lovato and Mel C.

But it wasn't until swapping California for Tayside 15 years later that his showbiz career took an unexpected turn, one which finds him as a gun for hire in the film, TV - and now - theatre industry.

It was another phonecall, this time from Irish writer and director John Carney , working on the development of 2016's Irish coming of age romcom Sing Street, which took Clark's musical career into unexpected territory.

"John's big brother used to turn him on to records, and one of them was Meet Danny Wilson (the band's 1987 debut LP)," says Clark.

"We'd never met before, but he remembered Danny Wilson, called me up and asked me if I would write a song and sent me a bunch of briefs. I saw one where a young girl was giving up on her dreams and a boy was trying to convince her not to. I wrote the song Dream For You, and John liked it so much he asked me to come on board to write the music for the film.

"But that song ended up being cut from the film."

No matter. While Sing Street, Carney's semi-autobiographical story of a teenage Dublin boy forming a band to win the heart of a girl, might not have made the same cultural impact as its tonal predecessors The Commitments and Oscar-winning busker flick Once, its burn has been slow and its music appreciated by folk who know their way round a good tune.

"@ GaryClarkMusic Killer tunes in Sing Street," posted Mark Ronson on Instagram. "I watched the entire end credits to see who wrote them."

"Sing Street is a great movie, and a great example of self-expression," wrote American rapper Tyler The Creator.

"Most films you'll see this year won't touch Sing Street," raved Bono, on U2's official website. "At the same stage, U2 weren't as good as the kids in Sing Street."

The music played by the kids in Sing Street is the music written by Gary Clark. Bono, Ronson and Tyler weren't the only ones to notice its quality.

The story also pricked the ears of the production team Carney had worked on with the theatre adaptation of Once.

Now adapted for the stage, it opens in New York at Manhattan's New York Theatre Workshop this week.

"When I saw the first scenes for it being workshopped I found it really emotional," says Clark, pondering the reality of his work landing at the epicentre of mainstream theatre. "I called John immediately and told him I thought it was going to be really good. There's such good writing there, and that's what I thought when I saw the film for the first time, too.

"John and Enda Walsh, who has developed it for stage have that sensibility that you just love the characters because you laugh with them and you hurt with them.

"It's that Irish wit, they really move you through these emotions quickly. It's a story which puts a lot of love into the world. It has a great heart.

"I told John at the time, when it didn't do as well as he'd been hoping in the cinema, that I thought it would eventually find its way to a lot of people, and that he'd just need to be patient. I'm usually wrong about these things, but in this case I think I was right.

"There seems to have been a real groundswell of younger people in particular who relate to the story, and I guess that was the impetus for them thinking it could work as a stage show."

The song which won him the gig has also made its way back into the story, adapted by Irish Tony-winning writer Walsh.

The film received largely positive reviews from critics and although it faltered at the box office, Clark soon started to see signs that his optimism over its impact was not misplaced.

He says: "I've a friend who lives in LA who told me a few years ago that her kids were having 'Sing Street Day' at school. They'd get dressed up in 1980s gear and sing the songs. That was the first hint I got about it catching on. And there are videos of kids doing their own versions of these songs on YouTube in their bedrooms. So you really get the feeling that something's happening. It's wonderful. I'm so glad it's getting another go out there, because I love the story and the songs we did."

With Carney chipping in from Dublin, Clark originally wrote the songs for Sing Street at his piano in his Broughty Ferry home, a world away from the bright lights of New York's theatreland.

His creative partnership with Carney has since yielded opportunities the songwriter would have been delusional to consider as he packed up his life in La-La land and headed back to Dundee.

Yet his evolution from reluctant popstar, to hitmaker in the shadows, to accidental writer for film, TV and Broadway musicals is all tethered to Carney's big brother's love for the first Danny Wilson album 32 odd years ago.

"I'm the only man who moved from Hollywood to Broughty Ferry to get into movies," Clark says, laughing. "I challenge you to find me another.

"I didn't know how to get into musical theatre and film and all that. It's something I always wanted to do, and although I've had a lot of songs placed in films, they're songs that already existed out there on records. This has been different, it's about writing for character to support the emotion of the story. You're working with a different trigger of inspiration. You're not sitting down thinking 'what am I going to say about me again?' It's such an exciting and inspiring world for me to work in."

One such trigger came in the shape of stories published in the New York Times and developed for the on-demand anthology TV series Modern Love, written and directed by Carney, with guest directors including Catastrophe's Sharon Horgan and Shameless US star Emmy Rossum.

With an original song in each episode, Clark had a formidable brief.

"It wasn't always easy," he says. "Some of the directors were aware of the concept, and some of them hadn't been told. In John's episodes, there was always a space carved out for a song. We tried them in different spots in the other ones, over the title or whatever. It was a long journey."

The songs, by turns breath-catchingly beautiful and laugh-out-loud funny, are performed by the likes of Nerina Pallot with Clark performing several himself.

"Actor Anne Hathaway sings one about falling in love with a man in the supermarket peach aisle in a high-camp homage to La La Land, which descends into a heart-wrenching tale of one woman's mental ill-health.

"Anne is a great singer," he says. "Her song had a semi-tone key lift in it, like a jokey American sit-com tune from the 1970s. I sang the demo and it was really hard to find that semi-tone, but she came in and sang it first time perfectly. I was blown away."

The series has been a word-of mouth hit on Amazon, with rumours of a second run to come ensuring Clark's 2020 will be busier, and presumably more creatively fulfilling, than his nascent days as a pop star 30 years ago.

Nanny McPhee's development continues with Emma Thompson due to direct the stage adaptation of the movie she starred in in, bringing the songs she honed with Clark ambling in Argyll to the spotlight, most likely starting in London's west end.

"Nanny McPhee is a fantasy piece, almost a fairytale, so I'm dealing with completely different concepts," he says. "There's one called Is It Wrong To Eat a Baby. So I'm definitely spreading my wings there."

His writing sessions with Thompson came about after the actor saw Sing Street, but Clark wasn't flattered into accepting the offer.

"Until I met Emma I wasn't sure if Nanny McPhee was for me, not because I didn't like it, but because I wasn't sure if I was the right person for it, musically.

"But when I met her, she was just so funny, intelligent and musical. She's a classically trained piano player. And when she told me song titles like Is It Wrong To Eat a Baby, I thought, 'this is going to be a lot of fun.'"

Clark rarely performs in public these days. He performed at the opening of the V&A in Dundee last year, supported Deacon Blue at Edinburgh Castle in 2017 and Danny Wilson performed at the Glasgow Hydro in 2014 for the Ryder Cup celebrations. He doesn't rule out the possibility of getting the band back together in the future, but as far as pop music goes, his focus is now on Dundee two-piece Hyyts.

"When I came back to Scotland I intended to develop artists on a little record label, before all this other stuff took off.

"That all grew into Hyyts who've just released their first major label EP with Warners, songs I wrote and produced with them.

"But I don't really have that much time to do much pop music. I'm not saying I'd never do a tour again, but time always gets taken over with something else."

It's a happy complaint, one he likely wouldn't have given a prayer for when his band split up three decades ago.

From Modern Love to Sing Street, there's a youthful sense of things that could have been, and might yet be. If the young Gary Clark, at the end of his first pop dream, could speak to himself now, what would he say?

"He'd probably ask what took so long," he says. "As a kid, I loved film, and theatre too. My dad was a big fan of all those classic musicals, Singing In The Ran, Guys and Dolls, On The Town. Both Kit and I were big fans of that, and there's a lot of musical theatre in our Danny Wilson stuff.

"So everything I've been doing before has led me to doing this now. And this feels like where I'm supposed to be."

Sing Street opens at New York Theatre Workshop on 16 December. Hyyts's EP, Eepee, is out now