He damaged his hands, ears and mind in the search for sonic salvation – and turned his colleagues' hair grey in the process. In an exclusive interview, Kevin Shields sounds off about Britop being a conspiracy, why the Mercury prize is a joke and the bland state of music today

The early-evening crowd in this cosy central London pub have no idea that a sonic sorcerer stands in their midst. His outward appearance offers few clues: mop of fag-ash-coloured curls, unspectacular spectacles, sturdy cagoule and sensible trousers. Little about Kevin Shields' gentle demeanour suggests he creates magical, mind-melting music that drives people to have uninhibited sex, guzzle weapons-grade drugs and soil themselves. Of which more shortly.

For now, he leans on the bar – a big man, XL T-shirt – and, in a soft Irish accent, orders himself a small gin and tonic and a bottle of mineral water. "Funny meeting a strange guy in a bar," he murmurs, giving an indication that he rarely grants interviews.

Before the interview begins, Shields offers up some small talk: how seeing the Ramones in a north-Dublin cinema changed his life; why he enjoyed contributing towards the Lost in Translation soundtrack ("lovely people"); how he always found Gary Glitter creepy ("with his big hairy chest"). At 50, Shields' life divides into three movements: he spent his first 10 years in Queens, New York, the next decade in Dublin and the remaining time in London. He doesn't have any kids – "I'd like them though."

Shields, it transpires, is a passionate, sometimes bewildering, conversationalist. The next two hours glide by as he discusses decibel levels, corporate control and the collective unconscious. His thoughts come in great torrents, swirl through the filters, then emerge retooled and refined. It's like a spoken word concert by My Bloody Valentine, the band he has helmed for the past 30 years. Yet it's mildly surprising he has shown up at all, let alone on time. He rarely gives interviews, and punctuality isn't a concept he embraces warmly.

His working methods similarly defy conventional scheduling. My Bloody Valentine's second album, 1991's Loveless, required two years and an estimated £250,000 to complete.

"I would say I'm patient rather than stubborn," Shields says of his difficult reputation. "I just want to produce the best music I can and if events conspire to interrupt that process or the circumstances aren't conducive then I just stop ... and wait. But how can I be stubborn about my own work? I want to do it. But when I know I can do something really good I will wait 10 years to do it."

It is said that during the making of Loveless, such was Shields' singularity, that Creation Records' bigwigs Dick Green and Alan McGee – to whom Shields was contracted – went grey and bald respectively overnight. "That wasn't my doing and I'm sure it didn't happen," Shields shrugs. "But wouldn't that be a great power to have?" He chuckles, then his jaw muscles bunch. "You know, people shouldn't sign bands like us if they don't want to take on that responsibility. It's like getting a pack of big dogs and not feeding them. We were taken on ... carelessly. I just wanted to focus on music but McGee and Green hadn't encountered someone like me before, a person that they couldn't control."

Wilful is the word you hear. Like Scott Walker and Mark Hollis, Shields is one of the few contemporary artists who marches to the beat of his own drum. But his vision has claimed victims: Shields has seen more breakdowns than an AA man. And if the making of Loveless was a song and dance, then the protracted process that led to its follow-up was a fully fledged fandango. Seventeen years in the making, m b v was released in February this year and was worth its wait in gold.

A poignant and powerful piece, m b v often bears closer comparison to abstract impressionist painters such as Mark Rothko. He is trying, Shields says, to convey "feelings above ideas". Every nuance and shadow of his music is minutely considered. Each frond of feedback lovingly tended. "And that stuff takes time," he smiles.

But when it is jokingly suggested that, had Shields released m b v in 1994, as initially planned, he could have kiboshed Britpop, his mood changes. "Britpop was massively pushed by the government," he says. "Someday it would be interesting to read all the MI5 files on Britpop. The wool was pulled right over everyone's eyes there."

So had he been invited to Downing Street during the swinging 90s, how would he have responded? "I would have agreed to go on condition that we could play a song," he says with a hint of menace. He's referring to MBV's formidable live sound. One reviewer complained that the experience had more in common with torture than entertainment. And while their shows are exceptionally loud – earplugs are given out ("it is not cool to damage your senses") – this is no heavy-metal bludgeoning. There are frequencies at play and physical energies shifting that do more than merely caramelise your vital organs.

"If you want to hear music played quietly, that's what record players are for," he says before conceding: "Back in 2008 we were very loud. It was kind of an experiment, something we'd always wanted to do. I heard people were coming out of those gigs looking like they'd just witnessed a car accident. But in a world where blandness and OK-ness is a dominant factor, to do anything that's a real experience is a positive thing."

Not so for the unfortunate soul in the lavatories at London's Town & Country Club on 15 December 1991. As MBV concluded their set with what they once termed the "holocaust section" of You Made Me Realise (read: punishing audio/eye-frying lights), a dismayed audience member realised that the pulverising sound had caused him to soil himself.

My Bloody Valentine in the 1990s. Photograph: CAMERA PRESS/Steve Double

"That can happen," sniffs Shields. "Although that's a very small percentage when you think about it: one person out of maybe 2,000. But there's always someone who'll shit themselves at the slightest excuse."

As if on cue, a sloshed suit squeezes past Shields en route to the gents. Shields apologises politely, interrupting as he does an impressive discourse on punk's post-1977 years. It's something he's quite the expert on: this, after all, was the era where punk underwent an industrial rethink and MBV's sound was forged. He eulogises pioneering Pil guitarist Keith Levene ("just sublime and utterly without ego") and Killing Joke's Geordie Walker ("this effortless playing producing a monstrous sound"). He even has a soft spot for the Cockney Rejects, pugnacious purveyors of football singalongs. "Great guitar," he marvels, fingering a bar-chord air riff. "And always for the greater good of the song."

This fondness for heads-down, balls-out boogie may help explain Shields' uncharacteristic extracurricular activities. Whereas resting rock stars traditionally retreat to Mustique to recharge their creative batteries or plan a dazzling electronic project with some Canadian, Shields took a sabbatical from My Bloody Valentine and went on tour with Primal Scream. A wise move in retrospect?

"Yes and no. I mean, I was terrible in my 30s. I did some silly, crazy things. That's when I really went for it in every respect. Taking drugs recreationally – lots of them. So it's all very hazy and jumbled up. I can remember the beginning and the last few gigs with Primal Scream but everything else is interchangeable.

"I once took down the name of every single member of staff on an aeroplane because I was so fucking drunk. I found this illegible piece of paper in my pocket the next day and couldn't work out what it was. I'd blacked out. But now I'm a more convivial drinker – I don't get really drunk. I still have a few pints of gin and tonic before I go onstage but nothing stupid."

Thirty years at the glittering coalface of alternative rock has finally provided security for Shields ("I've been OK for money since about 2008"), but has taken its toll spiritually and bodily. Periods of seclusion and depression have invited parallels with his hero Brian Wilson. And while his work was always painstaking, it has also become painful.

Shields suffers from tinnitus ("it varies from mild to extreme") and has tendonitis in his fretting hand. He dismisses these conditions philosophically – "It's part of the job and we're all going to die anyway" – but when the tinnitus struck for the first time during the mixing of Loveless, he feared for his ears.

"Initially, I was worried," he admits. "But I've come to treat the tinnitus as a friend. It filters unwanted sounds and actually protects my ears. It becomes your first line of defence against audible stress. I'm not boasting because my hearing has always been average but I hear things that a lot of people don't hear. That part of my brain that processes sound works a lot harder than average.

"With the hand," he says, extending his long left thumb, "I kind of play through the pain and it stops. I ignore it. Once you start to immerse yourself in the sound, any discomfort just disappears."

The band on tour in 1991. Photograph: Hulton Archive

Precisely how Shields achieves his queasy, waking-state guitar sound has long been the subject of stubbly examination. "A very loose taped-up tremolo arm on a Fender Jazzmaster, open chording and a few effects," is as far as he will be drawn. "It just happens. It's really like magic. It's more the zone, the meditative state I get into. It has very emotional connotations for me. I have to keep very still when I'm playing. I can't explain it. It is magic.

"I see music," he adds. "I remember music visually rather than sonically. Colours and shapes moving through each other."

And how would Shields, a control freak – let's be frank – prefer people listened to his recorded output?

"However they like!" he says, before reconsidering. "But perhaps not with headphones. It wasn't made to be listened to on headphones."

Is it true that MBV's music makes a good accompaniment to sex? "People have said that," he nods. "It's sensuous. Sensuality has informed a lot of what we do."

Has he ever had sex to his own music? "Not on purpose, put it that way," he says with a grin. "Although our music is not so great on acid. It's too dense, I think. It doesn't have that acidy space context. It was always more of an ecstasy thing."

With all the drugs, the psychological pressure and physical pain, the psyche-scouring, the perfectionist production values, the pints of gin and tonic, has Shields ever worried that he might lose his mind?

"I purposely melted my mind," he says. "It felt like a way of seeing the world in a different way from normal. It's complicated but I explored the nature of consciousness. I attempted to tune into the Earth's frequency – which is about seven hertz, I think. It sounds like a load of shit. But I've been searching my inner self, I suppose. And it's made me stronger. I think you can hear that in the music."

If you worry that one of music's chief noiseniks is getting a bit hippy-dippy then Shields soon dispels such fears. Abruptly detuning from the elemental megahertz, he launches into a seething diatribe against the Mercury awards and their reluctance to acknowledge "truly independent artists".

m b v was, apparently, not even considered for a Mercury nomination on the grounds that qualifying albums had to have "a digital and physical distribution deal in place in the UK". m b v was self-released, with the digital version available only through the band's own website. "In their eyes," he concludes, after a lengthy, comma-free rant, "what we're doing is illegal. Not within 'the rules'. We don't exist."

"There are sinister forces at work," he adds. "Our freedom is diminishing. The rightwing is creeping in like water. That's got to stop." Then, zipping his cagoule purposefully, this sonic sorcerer and eccentric sweetheart issues a parting shot.

"Personally," he smiles. "I intend to react to it most disrespectfully."

My Bloody Valentine: essential tracks

1. You Made Me Realise

(single, 1988)

No MBV show is complete without this glitterball demolition.

2. Off Your Face

(Glider EP, 1990)

The unmistakable sound of pre-puking student omnipotence neatly distilled.

3. Soon

(Loveless, 1991)

When shoegazing shuffled self-consciously towards the dancefloor… and dazzled!

4. Wonder 2

(m b v 2013)

Pushing the drum and bass envelope. Through satan's letterbox.

5. Nothing Is

(m b v)

Machine-tooled rockabilly. So compelling you're sad when the relentless exuberance stops.