It’s just after 9am in Forest Hill in South London. The denizens of this leafy area have walked their children to school and boarded their commuter trains. In David Mach’s messy but unfussy two-floored studio, two handfuls of assistants and technicians have had their orders for the day and are buzzing around huge, collaged canvases, drawing boards and storage drawers.

Upstairs, Mach sits across from me, manically flicking through the recent issue of The List and The List’s Eating and Drinking Guide that he requested I bring. ‘I’m looking for pictures I can use,’ he says. ‘I ask people to bring me magazines and I sit there ripping them up as we talk, you’re always looking for that new image when you do collage, something fresh. For me it’s like listening to the news or keeping up with world events. It can be the beginning of my day sometimes, just ripping stuff out.’

Tall, scrawny and angular, Mach could be John Byrne’s younger brother or Shaggy from Scooby Doo, now slightly greying but still chasing ghosts. Almost two score years of living and working in London – far longer than he lived in his hometown of Methil in Fife – have not altered the ‘scoop’ – the perceptible rise in vowel sounds – or the sharply up, gradually down sing-songyness of his Fife accent.

‘It’s a major sin to leave and go and live in London. I’ve lived here longer than I lived in Scotland but I never feel away from the place, which is quite odd.’ He grimaces into his coffee mug. ‘You can interpret that any way you like: “I’m working class and Scottish, blah blah.” But that’s still how I feel, I go to events now and people still ask me how long I’m staying down for and I point out that I’ve lived here for 35 years.’

Contrary, funny and wilfully unpretentious, Mach has been out of the art world spotlight for far too long. Having spent most of the 1980s and 90s garnering acclaim and controversy in equal measure for his huge, so-called ‘public art’ sculptures and installations featuring textually rich, mass-produced objects such as tyres (1983’s Polaris) or magazines (Adding Fuel to the Fire, Barcelona, 1990). Mach’s last high-profile piece in the UK was for New Labour’s Millennium Dome: ‘We did a 100 ft-long, stupidly detailed portrait of the nation, which I hated. Portrait of the nation, for fuck’s sake, makes it sound like Tony Blair speak, doesn’t apply to us at all.’ Mach smirks like a naughty school kid, before settling into what feels like a well-practised rant.

‘A weird thing has happened to me because I used to work exhibition after exhibition, but I actually work way more now and do an awful lot less exhibitions. A lot of it is solo commissions or corporate commissions. People think I have crossed over from public art to commercial art but I think I’ve always been commercial. I remember being in New York and this guy says to me, “I love your work, it’s great, but it’s a shame you don’t have anything to sell.” It was like a knife to my heart. I thought someone was going to buy this 100-tonne magazine sculpture, that was me being commercial, as much as I am commercial now, it may look like lunacy to most but that’s just the way I go after these things.’

Five years in the making, Mach’s first major Scottish exhibition for some time deals with the always thorny issue of religion. The agnostic son of a devoutly Christian mother and an atheist father, Mach may have inherited a certain masochistic Protestant work ethic but The King James Bible is hardly a natural fit for him.

‘The Millennium Dome project was exhausting and I didn’t feel like launching myself into something immediately, but a seed had been sown. A few years later I was driving through Glenrothes with a teaching colleague and friend and we are talking about ideas for projects and stuff and she said: “You should do The King James Bible,” and I said, “Fuck, yeah I should.” It took me eight years to get the thing going but this was before we knew its 400th anniversary was coming up. It took me a long time to mull it over but meanwhile I’m collecting things that made their way into the final show, so in a way I was compiling the material subconsciously. I went through the Bible looking for quotes to guide my collages and realised I knew so much of it because of a religious upbringing but I was also struck by how much The King James Bible is about how we speak now, the language of today comes off those pages.’

Mach stops to drain his coffee mug. ‘And then you take the plunge and loads of stuff happens because it’s costing a bloody fortune to make it because so many guys are involved. Since 2008 we’ve been working on this exhibition here, up in Scotland and over in Deptford where we have another studio. Plus you’re producing books, catalogues, postcards – you name it, you have to have the money to spend on it and then decide that you are not gonna spend it on a nice house in the country or a nice car but on this. For a long time you end up thinking, “Why the fuck am I doing this anyway?”’

Mach, who could well be responsible for the Festival’s blockbuster show, is very happy to be utilising the capital’s undervalued City Art Centre. ‘Art-wise, the City Art Centre is the only bit of Glasgow in Edinburgh. It’s got that kind of edge to it. It’s also a difficult space, it’s got a great first couple of floors there but the rest of it is more “regular”, shall we say. I love the challenges it presents. For instance, at the beginning of this whole process, I was told that the downstairs was to become a shop space and I thought, “Fuck, that’s the best space they’ve got,” and I thought, “Shit, I’m gonna have to rethink this now.” And then, after a while, you think, “Actually, I quite like that.” It’s a difficult show anyway, it’s a kind of religious show, a show about religion and art and you have a bloody shop right in the middle, a bloody retail space right next to these big fuck off collages and crucifixion pieces, that’s the reality of the situation. I like that. I’ve always hated that idea of working in galleries and museums where the curators or whoever is running these places treat the space like they are bloody churches and that they are high priests of blah blah blah.’ He laughs. ‘It’s still a special cultural place, it’s not like I’m showing a pile of rubble in Beirut or something.’

Mach will be working on-site for the entirety of the Festival, turning one floor of the gallery into a studio. ‘We are going to make a Last Supper,’ he boasts. Will he be inviting Alex Salmond to sit for him?

‘No way!’ He smiles. ‘But we’re gonna have a second opening when it’s finished so we may invite him then.’

With exhibitions coming up in Dubai and Hong Kong plus new international commissions for his giant gorillas and stags, Mach is a busy man, but that doesn’t stop him ruminating on a future project. ‘After The King James Bible I’d really like to tackle The Kama Sutra. Now there’s something I’d really like to get my teeth into. If you’ll pardon the pun.’ And a deep chuckle pierces the mid-morning lull.

David Mach: Precious Light, City Art Centre, Market Street, 0131 529 3993, 30 Jul–16 Oct, £5 (£3.50).