It is a quiet Thursday morning, and John Lydon and I are talking bollocks. Specifically, we’re discussing a song called Shoom, the final track on What The World Needs Now..., the new album from Public Image Ltd, the great, scarred, mutant vessel Lydon has steered bloody-mindedly since 1978, when he jumped ship from the Sex Pistols.

In Shoom – the song is named after the skewwhiff pulse of its wonky drum machine – Lydon dances a crouched two-step with the word “bollocks”, using it to batter everything in his path. “F*** sex,” he mutter-sings, sounding like a tense electro Albert Steptoe, “it’s bollocks. Success: it’s bollocks. Contracts: well, they are bollocks. Botox: f***ing bollocks...” On it goes, until suddenly, breaking into the high, broken Lydon wail, he lets fly with the line that gives the album its title: “What the world needs now… is another… F*** OFF!”

Hearing this, you might reckon it’s just Johnny being rotten, showing off with his rude words. “Well, I’ve earned the right,” he says, referring to the day in 1977 he sat in a Nottingham courtroom watching John Mortimer, the beloved barrister and Rumpole Of The Bailey author, successfully defend the Pistols’ right to call an album Never Mind The Bollocks against indecency charges.

“And having earned that right,” he cackles, “it’s up to me to wear out its welcome!”

Actually, though, as often with Lydon, what you might think is happening is not what’s happening at all. This Shoom isn’t just gleeful obnoxious obscenity.

“It’s my dad,” he says. “His death was still in my mind in the studio, and I wanted to write something specifically for him. That song is from my old man’s point of view: the way he used to sit in the pub, this very dry, brilliant sense of timing and humour, always brittle, but deeply funny. It’s there in that song, that’s the personality I fondly remember. It’s everything about him. Except his Irish accent. My dad in my voice.”

This explains the ragged edge to Lydon’s voice when he cries that chorus. He lost his father suddenly in 2008. What his world needs is to hear him one more time.

“This person’s had enough of useless memories,” Lydon declared through the dubby miasma of Metal Box, the cavernously claustrophobic 1979 PiL album many consider his masterpiece. (“Yeah: well, they didn’t at the time.”) But memories keep resounding in his songs. In its cranky way, Shoom is a flipside to Metal Box’s Death Disco, a juddering post-punk floor-filler built from depth-charge bass, Lydon’s thorn-in-the-soul screaming, and guitar that wraps like wire around the theme from Swan Lake and strangles it.

Some took the Tchaikovsky reference as a two-fingered salute to high culture, a snotty parody stomp. (“Just another con-game?” pondered the NME’s review. “A gigantic p***-take?”) In fact, the song is deadly serious. The thing Lydon is screaming about is watching his mother die in her hospital bed: Swan Lake is there, being torn apart, because she loved the melody. To this day when PiL perform, there is no distance between Lydon and Death Disco. It’s not uncommon to see tears in his eyes.

“The songs, they’re all about specific scenarios in my life, or things that struck me deeply. They take me back there. It’s my photograph album. Some are sometimes overwhelming to perform to the utmost – because that really hurts. But it’s essential.”

Music is what John Lydon is about, although it is often the last thing anyone wants to ask him about. In Britain, especially, it can sometimes seem as if the media wants him to replay the Pistols’ Bill Grundy interview on infinite loop: the moment Grundy goaded, “Say something outrageous.” Since he first appeared, he’s been held up as monster, provocateur and cartoon – all roles he’s been willing to play, of course. But the deeply personal nature of PiL gets discounted, overlooked.

“I get journalists putting in their spiky little nonsenses, saying it’s all some elaborate joke on my part. Well... that’s an expensive joke, isn’t it? It’s a spiteful thing to say. This is no joke to me. Never, ever has been. This is what I am.”

Taking him through the years – sometimes taking him back – PiL has been Lydon’s Tardis in reverse. While he remains constant, it keeps changing shape around him, an experimental lab exploding through countless styles, internal arguments and umpteen line-ups. And, like Doctor Who, it suffered its own 20-year hiatus. The last PiL record, 2012’s defiant This Is PiL, was the first since 1992.

Broken only by a 1997 solo album (“I put that out under my name because it is just me: I couldn’t afford a band”), Lydon’s two-decade recording silence was the result of contractual wrangling with his old label, Virgin. The TV stints and the butter ads helped him buy himself out, then fund an unexpected, triumphant tour for a reactivated PiL in 2009. Proceeds from that allowed the self-financing band to make the 2012 album on their own independent label – which funded another tour, which funded the new record.

Work on What The World Needs Now… coincided with a particularly busy period in Lydon’s life. For one thing, there was the matter of his becoming an American citizen, late in 2013. He first moved to the US over 30 years ago. “Before that, I’d always been led to believe Americans were just gaudy, just into baubles and flash cars. I discovered that need not be the case.”

The decision to apply for citizenship came partly as a response to recent political developments. “I wanted to show some commitment to ObamaCare, really, which is a wonderful step in the right direction for America. But now I’m looking at Donald Trump trying to buy the Presidency, and that absolutely revolts and terrifies me. A very interesting election coming up, though. Haven’t I picked the right time to be in Rome? And I shall be voting!”

Making the album also overlapped with finishing last year’s Anger Is An Energy, Lydon’s second volume of autobiography. He found the two bleeding together. The book revisits one of his formative experiences: when, aged seven, he contracted meningitis and fell into a six-month coma, waking to discover he had no memory of who his parents were. That memory of having no memories resurfaces on the album’s I’m Not Satisfied.

“We improvise a lot, and that happened instinctively in the studio. And, yeah, it’s completely me as a young child, screaming: ‘Why don’t I remember your name?’ That whole time, recovering from that, seeing my parents as strangers, that lasted nearly four years. That’s a very painful lesson, that complete sense of isolation.”

His greatest fear is still that it might happen again. “Just before I go to sleep, every night, I’m always thinking about that. What if I get into that condition again? Would I be able to handle it as an adult?”

As it is, sleep is a productive time for him. “I’m always writing, y’know? I keep a notebook by the bed. When I have dreams, I’ve learned to wake myself and write it down. It can be amazing. You go back to sleep feeling quite content. Then you surprise yourself when you wake up and find it – all this stuff that was going on inside you, that you’re not aware of anymore. There’s a lot of dreamscape in me.”

Before speaking with Lydon, I was thinking about another time I interviewed him. It was July 7, 2009 and, while we spoke, Michael Jackson’s memorial service was being beamed live around the world.

“Another stupid rock death,” Lydon said as coverage unfolded on TV. “It really annoys me, how he ended up so isolated. It’s just not right. Y’know, people end up like this if they’re not careful. Fame is not a good thing. It’s very f***ing dangerous. And ego isn’t the problem – it’s the isolation after. When you come off stage, it’s… nothing. It’s nothing.”

Recalling that conversation, and with a new PiL tour looming, I ask how he feels before he goes on stage today.

“Oh. Terror. Nerves shaking. Really. Feeling like I could heave. These days, I find I’m going on stage with a completely open heart – and that’s a frightening thing, because, over the years, I’ve used various personas to protect myself. It’s scary letting go of that. It’s begging for someone to cause me mental pain, with a negative judgement, or with me making a fool of myself. But I wouldn’t be worth tuppence if I didn’t face up to my own flaws and weaknesses.”

And after a show? “Drained. Impossible to sleep. Still vibrating with tension. Aaaaaand… then it all starts again 6.30am the next morning.”

And during a show?

“Oh, once out there – well, that’s different. All that tension is released. I can be myself. You leave ego in the dressing room. You know you asked about Death Disco? When I’m doing that, for example, oddly, there’s a reward in going through it again and again. That song, it’s different every time, but sometimes I clue into something that helps relieve the pain and the stress.

“And I can sometimes see this in people’s faces. I like an audience to be lit, to see them. I can gauge if they’re understanding what I’m trying to translate. That empathy, that’s dramatic. That’s really what all this – music – is supposed to be about.”

What The World Needs Now is released September 4 on PiL Official. Public Image Ltd play 02 ABC, Glasgow on September 18