“I can't emphasise enough, I had no one,” says young Scottish songwriter Katie Gregson-MacLeod of the story behind her meteoric rise, thanks to the overwhelming response to Complex, a song she put on TikTok over the summer. “This was an anomaly and it still is, just a video of a song I'd written three nights before, a 45-second clip of the chorus. I do every job myself, marketing, promotion and consistently posting on social media.

“I’d throw everything at the wall and see what stuck, but there wasn't much conscious thought behind it. I popped the video up, then the next morning woke up to 150,000 views. It was also the people that were commenting… I was like, how the heck are Maisie Peters, Lennon Stella and Gracie Abrams all seeing this? Stuff just catches on like that, algorithms are very weird.”

She had likes from some of the most famous young singer-songwriters in the world, all roughly her age, but still Gregson-MacLeod had to go to work in an Edinburgh coffee shop that day. “Yeah, of course, I had to do a shift,” she says. “That whole week was the strangest of my life, though. I'm on the phone to people, I'm being messaged by labels, but I have to make Americanos all day. It was bizarre.”

Raised in Inverness, Gregson-MacLeod’s mum was very musical, just like her daughter, although the young singer’s attention was split by playing squash to a high level in her teens. At 16 she decided to focus on music, and after moving to study history at the University of Edinburgh (she’s deferred her final year) she played at venues including Sneaky Pete’s, the Mash House and King Tut’s in Glasgow, including support slots for artists like Eloise, William Prince and Be Charlotte.

Now she’s signed to Columbia, and after releasing a demo version of Complex recorded at Post Electric in Edinburgh, Idlewild’s Rod Jones’ studio, a version produced by Greg Kurstin also emerged; Columbia and Kurstin are the label and producer behind Adele.

“Greg was a big fan of the song when he heard it,” she says. “He put this absolutely understated, light hand on it, it did exactly what it needed. I recorded new vocal and piano takes, but he heard the Post Electric demo and said ‘that's the exact emotion I want’, so he used that.”

What about Complex itself, which she’s recorded as her Scotsman Session? “I wrote it quickly in a very reflective state,” she says. “It was one of those moments where you reflect upon years’ worth of moments, with resignation as the main emotion. It’s a weird one to talk about… I've had relationships where I’ve been attached to somebody that's just not on the same page, but the chorus is the question of what am I responsible for versus what are they responsible for? Is this the role awful people have had in my life, or are they not that bad? It just spilled out.”

After the song’s success she’s now writing again, with an eye on an album. “Progress I would have never imagined over a ten-year period has happened in three months,” she says. “Which is terrifying, and it can be overwhelming, but it's also incredibly life-affirming. I feel like a lottery winner.”

Katie Gregson-MacLeod launches her ‘Songs Written for Piano’ EP at the Pleasance Theatre, Edinburgh, on 2 December, see www.katiegregsonmacleod.weebly.com

The Scotsman Sessions #341: Katie Gregson-MacLeod