As singer with the Happy Mondays Shaun Ryder used to do a lot of drugs. But that doesn't explain the encounters with aliens he has turned into a new TV show, he insists

Shaun Ryder was 15 when he first saw one. He'd just started as a messenger boy at the post office, and was walking to the bus stop on Hilton Lane, Little Hulton. It was 6.45am, pitch black when he looked up into the sky. "At first it was still, and then it went, 'Voooooooom!' And then again: 'Voooooooom!' Classic zig-zag, hovered, then went off at 10,000 miles an hour. Like Star Trek. Boom. Gone. Yeah!"

Another bus stop a few months later in 1978. This time he's at Irlams o' Th' Height in Salford, it's around 5pm. "Hundreds of lights going across the sky really slow, and I'm thinking, 'God, are we being invaded?' The next day in the papers it said: 'Mysterious lights in the sky – lights at Salford rugby ground have gone mad.' And that was bullshit because when the lights at rugby grounds start moving around, it's nothing like these."

Ever since, Ryder has been obsessed with Ufology and extraterrestrial forms of life. The former Happy Mondays and Black Grape frontman gets narked with people who assume he was off his head when he saw his UFOs. Fair enough, he has spent much of his life off his head, but he insists that any time he's seen anything otherworldly he's been clean and sober.

Ryder, 50, defined the Madchester era of ecstacy-inspired dance music in the 1980s. He ranted his brilliant nonsense lyrics ("You're twistin' my melon man/ You know you talk so hip man/ You're twistin' my melon man") to an inspired, jingly-jangly rock-funk-northern-soul-house-hiphop backdrop, and somehow managed to combine pop stardom with crack-dealing and drug-fuelled psychosis. Then, in 2010, he found populist redemption in the Australian jungle with Ant and Dec and became an unlikely national treasure. Before that, television producers were terrified of what he might come out with before the watershed. He was regarded as a liability. After I'm a Celebrity, they couldn't get enough of the newly cuddly Ryder. With all the drugs he'd ingested, he should have been dead; but here he was back with spanking new teeth, a family-friendly smile, and great patter. He was invited to go on numerous reality shows, but turned them down. So telly people asked what they could do to get him back on air. UFOs, he said. And aliens.

Two years after he started investigating UFOs, Ryder is back as an author and documentary film-maker, having travelled the world looking for spooky sightings. His conclusion? He's more convinced than ever that we are not alone.

Ryder makes a convincing presenter – warm, engaging, a bit bonkers, spooked, occasionally sceptical, never cynical. He has travelled to Chile, where more UFOs have been spotted than anywhere else in the world, hooked up with legendary abductee Travis Walton, and met a perfectly normal Yorkshire family who tell him about the dazzling UFO that almost blinded them on the way back from a meal out at The Little Chef.

I ask Ryder if he went out there determined to prove that his childhood experiences were real. He looks at me with stary eyes. "It's not that I want to believe, it's just impossible not to." His voice is getting louder. "We're not the only life in the universe. We're just not. It's ridiculously impossible. If you look at the way kids are being taught now … when I was a kid at school, you was taught there was no life out there – that was it. But now kids are being taught there's water, so where there's water there will be life forms or whatever. So it's not that I want to believe, that's how it is."

He puffs hard on his electronic cigarette. No drugs these days for Ryder. He knows he can't cope with them. Funny thing is, he says, his dad can sit at home spliffing the day away, but not him. Just electronic fags, and the occasional real one. "I've gone from smoking 25 a day to about five 'cos of these. It wasn't really that I wanted to give up smoking, it's just that you can't smoke anywhere these days. The first one I got, you didn't really get the hard hit at the back, so I got these ultra ones. And these are just the best."

'Some of the people I've met are mad as a box of frogs' … Shaun Ryder on stage in 1999. Photograph: Christopher Thomond for the Guardian

He inhales joyously, and talks about the road trip he went on with Travis Walton. In 1975 Walton was a logger when he and his crew came across a luminous flying saucer in a remote part of Arizona. The terrified crew raced to their wagon and got the hell out. When they realised they had left Walton behind, they went back to look for him. There was no sign of him. They went into town and reported the incident to the deputy sherriff. For days the whole town searched. Nothing. Five days later he reappeared and said he had been abducted by aliens. Over the years he and the crew have passed numerous polygraph tests. Walton, a man with heavy, bloodshot eyes and a lugubrious moustache, is still haunted by his expereince. "He looked like he's got post-traumatic stress disorder, like he'd walked into Vietnam, and spent two years there and come out," Ryder says. "Just imagine, even if one appeared in front of you, it would traumatise you properly. You'd go grey. Your whole world would change. Everything. It's just day one again. So you're going to look traumatised. And you spend some time with him and you just know."

Ryder and Walton make for an unlikely team, but they strike up a melancholy rapport. As a 29-year-old, Ryder says, Walton believed he'd been kidnapped and experimented on by a malign force. But now, like so many people who have come into contact with extraterrestrials, he believes they were kind; that they probably saved his life. "Now he reckons he was hit by some sort of forcefield that probably stopped his heart. These guys then took him inside and give him some medical treatmentand then let him go. That's how he looks at it now. As he's got older, he's changed how he feels about it." That's the thing, Ryder, says – for decades, everybody assumed extraterrestrials are the enemy, but it's obvious that they're not. "These guys have got technology that's millions of years in advance of us, and if you think about it, they could have took us out just like that, and they haven't. They're certainly not hostile. We wouldn't be here if they were."

Ryder is far from convinced by everybody he met. Some Ufologists are just chancers out there for the fantasy ride. He knows they've not seen the real thing because they are too glib about it. "They say: 'Yes, I've been abducted, wahey! Wahoo! Some of the people I've met are mad as a box of frogs."

When he was young, did his interest in UFOs make him want to experience more out-of-body experiences through drugs? He answers in a typical round-the-houses Ryder way. "Well, see, here's the weird thing. From being a little kid, I've always been interested in space. Star Trek and Close Encounters – not Star Wars." He spits out "Star Wars" with contempt. "Skies, stars, the moon landing – even as a six-year-old I was glued to that. So I've always been interested in that. And then when I had my first acid trip, did it open my brain even further? Of course it did." Did his fascination with space make him interested in science at school? He laughs. "No, I was a thick kid, I didn't even learn me alphabet til I was 20-odd, I was too busy doing something else. I had a platinum fucking disc before I learned me alphabet. I grew up in the 60s and 70s, where it was still acceptable to say, 'Well, you're not academic, so that's fine, you'll do it some other way.' Nowadays it's like everybody's got to be academic. My kids are – they can spell, they can punctuate. My 11-year-old can spell anything. My lad Oliver is 19 and he's going to do music law."

It's amazing that he was illiterate and is now an author. Ah, Ryder says, well, if he's being strictly honest, the writing's not really down to him, that's his ghostwriter, the journalist Luke Bainbridge. In fact, Ryder says, the first time he looked at the proofs of What Planet Am I On?, the book accompanying the series, he got a bit of a shock, because Bainbridge had captured his voice too accurately. "Here's the thing," he says. "We're doing a book, and the TV show is PG – it can be shown in the day to kids on the History channel. So you want a book to accompany the TV series. So I get a draft of the book and it's, 'fucking this, fucking that, fucking dick, fuckin twat,' and I'm like, 'Luke! You can't!' I'm not very proud of me grammar, of me fucking vocabulary, but with a book here to accompany the TV series, don't be 'Fuck that fuckin' fuckin' fuckin' alien, this fuckin' here, that cunt there'. You know what I mean?" So you had to de-fuck it? He grins. "Aye, I had to de-fuck it."

'We’re not the only life in the universe. We’re just not. It’s ridiculously impossible' … Shaun Ryder. Photograph: Radford/Fortean/TopFoto

Do his family and friends share his passion for UFOs? "No, not really." His manager, Warren, is sitting in the room with us. He went on the trip to Chile with Ryder. Is he a believer? "No, he's not."

In Chile his team photographed something flitting across the sky that Ryder thought was a UFO at the time, but now he's not so sure. Does that mean he hasn't seen any since his teens? He doesn't answer. He looks at Warren for advice, suddenly coy. "I'm gonna say yeah … even though that's not strictly true."

What d'you mean, I say. You can't lie to me.

"Nonononono." He looks at Warren, unnerved. "Should I tell him because this is just going to look like bullshit?"

We're here for the truth, I say.

His sentences become disjointed. "Well, all I'll tell yous, right, is that I've seen one, really close up, about 50 foot above, and it looks like a cartoon. It doesn't look real. It looks like it's made out of Airfix kit. They look like toys. When you've seen something as close as I've seen – and bullshit drink, drugs, bollox, none of it, absolutely normal and straight – and you see it and you know they're here … "

Tell me more, I say. "I can't go into any more detail, apart from that it was literally 50 foot above me." Did he have any contact with it? "No, no, but the thing is I wasn't frightened one bit. I was very peaceful and placid when I was looking at the thing." He says it happened after he finished making the documentary series.

Are you not telling me the full version because you're saving it for a new show?

"No, I'm not telling you because if I start coming out with that story now, it will be, 'Oh I hear you've got a show now and you're just promoting it …'" He comes to a stop. "I thought someone was playing a fucking joke. I thought someone had made something out of a gigantic 40-foot Airfix kit."

Has the latest sighting changed him? "Yeah, it's made me think all sorts of shit. If you've seen something 50 foot away, right, and it's as clear as daylight, it really does make you think. It was early morning. It was ironic that I go out doing this show, looking in certain hotspots, and then boom! You see it here! How no one in the Swinton Worsley bit of Salford can not have seen that craft, only me, is beyond belief."

At one point, in the TV series, he says he thinks he quite fancies being abducted. I ask him whether, if aliens had come out of this ship and taken him off, he would really have been so blasé? I notice beads of sweat on his forehead. The sweat quickly spreads down his neck. He looks genuinely terrified. "Phrrrrrrr," he says, grabbing his upper arms. "I mean, I really wouldn't like to be taken from anywhere without giving permission. I wouldn't like to be just fuckin' zapped up and took off, and think 'This is great.' I would absolutely freak."

Shaun Ryder on UFOs starts on History on Sunday 10 November, 8pm.