CRAIG Armstrong must be one of the busiest composers on the music scene today – but he doesn’t really want to be. Not just now, anyway.

Over the last 20 years, the soft-spoken father-of-four has been in continuous demand in the movie world, the first-call composer for directors as diverse as fellow Glaswegian Peter Mullan, who has had Armstrong scores for all of his films, and Baz Luhrmann, with whom he has collaborated on such cinematic spectacles as Moulin Rouge! and The Great Gatsby. But recently he began to cut back on the film jobs in order to spend more time on his own music, and with his family, and less time on assignments from other people.

“I’m nearly 60,” Armstrong, an OBE, explains, “and I’ve always moved from project to project but now I’m thinking more about what I might want to do next. I’m taking stock of what’s important. Working on films is a big investment of your time – Baz’s films take two years! – so I’m trying to be more selective.”

The latest result of this is Sun On You, Armstrong’s first album on the Decca label – and one which, for him, represents the fact that he has “gone full circle” by going back to doing what he describes as his own music. What’s different, however, to the experiences that the young Craig Armstrong might have had when making such an album is that Sun On You was only heard by the record company once it was completely finished to his own satisfaction.

“The way I write now is to write the record I want,” he says, “rather than having lots of people influencing it. A few years ago I did an opera, The Lady From the Sea, with Scottish Opera. It was a long, protracted job. After that, I just wanted to write a very straightforward album, something that I’d want to listen to, something that was simple – simple in terms of sticking to just piano and strings, even though in my studio I’m surrounded by electronics, and there’s always the temptation to include them.

“I made the record myself, and let the record company hear it afterwards – so there was no influence or interference, and I knew that if people didn’t like it, at least I knew that I was happy with it!”

Could it be that this way of operating – with full artistic control – with his contemporary classical music is a useful complement or antidote to the film side of his work? “Probably,” laughs Armstrong quietly. “There are so many variables when you’re doing films – so many disciplines involved, from the acting, to the script, to the direction etc - it’s a small miracle when it all comes together!”

Featuring Armstrong on piano with the strings of the Scottish Ensemble, the compositions from Sun On You were premiered at Glasgow’s Fruitmarket in May, to a highly appreciative audience. The impression was of music which captures and evokes emotion – an aspect Armstrong says is inspired by abstract paintings, such as those by Rothco . It is also, perhaps unsurprisingly, quite cinematic - though still distinct from Armstrong’s film scores which tend to be more melodic.

“Yes, Sun On You is quite filmic,” he agrees. “I don’t mind when the film and classical stuff blur and bleed into each other. You just see where it goes. After three or four weeks, there were 14 tracks and I thought that they worked. The trick is to not go back, to not tinker – to trust your first instinct, because that’s what was in your head at the time.”

So it is that the compositions on Sun On You remain instrumental but one of them, Marelle, also now exists as a song – Cornflower – with lyrics by Elbow’s Guy Garvey who has also recorded it with Armstrong. It was released as a single late last month, and Armstrong is delighted with it. “I have never had a rigid plan in my career; I’ve always followed my instinct and if something feels right – such as a collaboration – then that’s fine. Guy Garvey and I had been talking about doing something together and then he heard the track and wanted to write a lyric. Sometimes magical things happen when you’re not being too rigid…”

Indeed. This isn’t the first time Armstrong has decided to cut back on his film work – he was actually talking about this 16 years ago in an interview with The Herald’s then-classical music critic Michael Tumelty. At that point, his youngest child - with whom his wife, Laura, had been pregnant when Armstrong was stranded in New York immediately following 9/11 - was still a babe-in-arms.

Back in late 2002, Armstrong – who had already won a mantelpiece-ful of awards from the film and music industries - was spending more time on his own music, having just completed a series of commissions for the Royal Scottish National Orchestra, to be conducted by the great Walter Weller.

Nevertheless, his steady stream of acclaimed scores resumed and such popular favourites as Love, Actually (2003) and Ray (2004), the biopic of Ray Charles, and The Incredible Hulk (2008) joined the Armstrong canon which already included The Bone Collector (1999), Best Laid Plans (1999) and Kiss of the Dragon (2001).

Much has been made of the fact that Armstrong landed the composing gig for The Quiet American (2002) because its star, Michael Caine, insisted on it. But how did Michael Caine come to be such a fan?

Armstrong chuckles. “The director, Phillip Noyce, is a major music buff. He loved The Space Between Us, the album I did on Massive Attack’s label, and he gave a copy to Michael Caine, who fell in love with one of the tracks, Laura’s Theme – and that’s how he came to say that he would only do the film if I was doing it too!”

Phillip Noyce is one of a number of notable directors who have visited Armstrong in Glasgow, and – says the composer mournfully – made the pilgrimage to the School of Art to admire its architecture. Who else has visited it? “Everybody! They all wanted to see it. Luc Besson, Baz, Jan de Bont, Oliver Stone …”

Of course, these big name directors have come to the city partly because Armstrong has resisted all attempts to persuade him to move to Los Angeles. Has he really never been tempted?

“It would certainly have been easier for work,” he admits, “and I do like LA. It gets a bit of a bad rap but musically it’s great – there are such incredible musicians there, and some fantastic jazz clubs and I’m a bit of a jazz fan. Purely and simply, when I put it to the kids, they had a meltdown – ‘We can’t leave our friends’ etc - so it didn’t happen.

“Instead, when I was working with Baz, and away in Australia for one or two months at a time, the kids would come out there to spend time with me. At the moment, I’m thinking a lot about Brexit – I’m so depressed about it. My wife is Italian and my kids are half-Italian. And I worry about what will happen to artists, and to Britain’s reputation.”

Those half-Italian kids are now pretty much grown up, and one of them has become a recording engineer, who has worked in LA and is currently working with his dad. “It’s quite handy for me,” says Armstrong proudly. “He’s a really good recording engineer.”

Armstrong senior has just been working on a British drama, Mrs Lowry and Me, about the “matchstick men” painter LS Lowry, played by Timothy Spall, and his relationship with his overbearing mother. “It’s been a really nice experience – and it’s a really good film. I’m a big fan of Vanessa Redgrave, who plays the mother, though I think I’d be a bit scared to meet her!”

Talking of visual artists, and the fact that Timothy Spall has played two (Lowry and Turner) in recent times, indirectly leads back to the subject of Charles Rennie Mackintosh – surely a much more dashing subject for a biopic and one which wouldn’t require Armstrong to travel? “That would be a GREAT film,” he laughs. “I’d be up for that!”

If anyone has the contacts to pull that one off, it is him …

Craig Armstrong – Sun On You – Music for Piano and Strings (Decca) is out now, and he plays music from the album at Union Chapel in London on September 11, with a number of special guests.