THE man who invented heavy metal is on the line. The man who, alongside bass player Geezer Butler, drummer Bill Ward and vocalist Ozzy Osbourne, thundered out of Birmingham in 1968 strafing the sky with round after round of gnarled riffs, siring hundreds upon hundreds of groups and changing the face of music for ever. The man who survived the bacchanalian excess of the 1970s and 80s when many of his friends did not. The man who ranks only slightly below Satan in the estimation of millions of metal disciples around the world.

“I just potter around,” says Tony Iommi when asked about his daily routine, his Black Country accent perfectly intact. Despite decades of globetrotting he still lives in the West Midlands with his fourth wife, Maria Sjoholm. The guitarist and chief songwriter in Black Sabbath is now 70 years old and called time on the band in 2017, five years after he was diagnosed with lymphoma, which was declared in remission in 2016. “I get up at 6.15am – which is very unlike me – and I have a regime of having my breakfast, taking the dog out, then I’ll play guitar for a while. The time just flies by. I’ve got a life now like everybody else.

“I have to be careful. I go to bed at a sensible hour. I have to anyway – I fall asleep if it’s late and I’m sitting down.” Iommi dissolves into laughter.

His longevity can be attributed in part to his positive outlook. “You’ve got to keep enjoying life,” he says. “Whatever it takes. I’m doing things now that I did in the 1970s – I’ve started collecting cars again. I’m buying cars I can’t f****** get in because they’re too low.” He laughs again. “It’s always been a passion – fast cars and stuff. I’ve got a Ferrari 488, a McLaren 650S and a Bentley Bentayga. I don’t want a hundred cars. I want ones I can use. I like them. I enjoy them.”

Precisely how much Sabbath fans wish to know about the contents of Iommi’s garage is open to debate but next weekend the son of Italian immigrants will be appearing in Paisley and Edinburgh with the acclaimed rock journalist Phil Alexander. Their conversations will undoubtedly dwell mainly on matters musical – and there is much to discuss.

Across five decades with Black Sabbath Iommi has worked with many of the biggest names in late 20th-century rock, including singers Glenn Hughes, Ronnie James Dio and Ian Gillan – who describes his year with Sabbath in the early 1980s in this month’s Mojo magazine as “the longest party of my life” – and drummers Cozy Powell (The Jeff Beck Group, Rainbow) and Bev Bevan (The Move, ELO). Sabbath alone made 19 studio albums, the best of which are generally accepted to be the first five – the eponymous debut, Paranoid, Master of Reality, Vol 4 and Sabbath Bloody Sabbath.

Is there a record Iommi thinks the group couldn’t have improved? “That’s a difficult question,” he replies after a long pause. “You always go ‘I could’ve done that’ or ‘I could’ve done this’ but I actually like the stuff we done with Dio as well – Heaven and Hell [released in 1980] and Mob Rules [1981]. I like those as well as the early Sabbath, of course.”

The ripple effect of those early records is hard to overstate. The list of bands who have acknowledged the colossal influence of Black Sabbath reads like a Who’s Who of rock and metal: Metallica, Van Halen, Iron Maiden, Nirvana, Guns N’ Roses, Soundgarden, Foo Fighters and countless others.

How does it feel to be responsible for so much music? “It’s fantastic,” he says. “I’d never have thought that would happen and it amazes me even now. It’s great to have been able to create something that’s still there after all these years and got bigger and bigger. The amount of bands I’ve met over the years from Metallica onwards who have praised me for coming up with the ideas has been brilliant. It’s almost a bit embarrassing.” Iommi laughs again.

At the core of the ideas to which he refers lies one thing: the riff. Having created the likes of Paranoid, Sweet Leaf, Supernaut and dozens of other staples of rehearsal rooms and guitar shops from Aberdeen to Adelaide, Iommi is the undisputed king of the metal riff – no mean feat considering he lost the tops of the ring and middle fingers on his right hand as a teenager and was advised by doctors to abandon his dream of playing guitar.

“If I’m coming up with a riff it has to really grab me and I have to go: ‘Yeah!’” he says, matter-of-factly. “I’ve got waylaid at certain times – with some of the stuff I look back and go ‘I could’ve done that better’ – but it’s something that grabs you when you come up with a riff. Is it a riff you can sing over or can it only be an opening riff? That’s how I work anyway.”

Who were the guitarists he was trying to emulate in the early days? “In them days there weren’t much around,” he replies. “There was [Led] Zeppelin and Cream – I liked [Eric] Clapton – and we done a few gigs in the early days with John Mayall, who I really liked. I liked blues played on a more modern sounding guitar, which was Clapton of course. That was sort of the way we went, only coming up with more doomy stuff.”

And where did those leanings come from? “It’s probably because I was so miserable,” he says, laughing. “No … It was one of those things. I used to love going to see horror films and Geezer and myself used to go to the midnight movies. We were trying to get the tension you have in a horror film.

“It’s funny because a few years ago I interviewed Sir Christopher Lee and he was going: ‘You are the king of heavy metal’ and all this stuff and I said: ‘Well, you’re the one who started it off.’”

Does Iommi still feel connected to the long-haired young guitarist trying to take a Hammer to electric blues? “Oh yeah,” he says. “It’s still within me. If I pick up a guitar now I’ll end up playing something doomy. I’ve got loads and loads and loads of riffs that I’ve got to get through so I still follow that same path. I put a lighter side on it as well – I do some acoustic stuff. I like both.”

While he misses performing, Iommi no longer wishes to revisit the lifestyle of the touring musician. “I love being on stage,” he says, “but I’ve had to stop touring because I can’t carry on finishing late and getting back to the hotel at five in the morning. It’s sad but I’m not writing myself off – I’m still well involved with playing, I’m still writing. I’ll be doing stuff soon but not so much touring.

“The older you get the more you feel it. When we were 20 we’d be up all night. We did try on the last tour but I was getting really tired.”

The road has taken its toll on many musicians of Iommi’s generation. Why do some survive and others don’t? “I don’t know. I’ve seen so many of my friends or people in the business who have done drugs and whatever else and died, from John Bonham onwards. John was a good friend. I’ve seen other friends go a similar way through drugs and alcohol abuse.

“You get lonely. You get bored in the hotel so you try to find something to do to be somewhere else. We saw it with Lemmy. He was the epitome of rock and roll. He was the one who would burn the candle at both ends all the time but at some point you’ve got to look at it and say, ‘I can’t do that any more.’”

Or the decision is taken out of your hands. “Absolutely, yeah. Even with Keith Richards, I’m amazed he’s still pottering on. I take my hat off to him.”

With his own hellraising days over, Iommi is both philosophical and upbeat about his past, present and future. “Music’s always been the love of my life,” he says. “It’s made my life and sometimes it’s caused me problems. When I was married before … Your music takes over and you end up being in the studio all night and touring and your marriage becomes lost, but now I’m very, very happy.”

Tony Iommi in Conversation with Phil Alexander is at Paisley Town Hall on Friday and Assembly Rooms, Edinburgh on Saturday. Visit thespree.co.uk and seetickets.com