When Slipknot first came over to the UK, there was a genuine fear they were going to corrupt a generation of teenagers.

The band, from Des Moines, Iowa, specialise in making the heaviest metal, and at the time of their self-titled debut in 1999, were nine strong, known by numbers rather than names, and wore matching orange, convict-style jumpsuits, while live shows sometimes saw members setting each other on fire.

They were, as frontman Corey Taylor, or #8 as he was known, admits, "every parents' worst nightmare".

More than their image and music back then, which largely involved Taylor's patented scream of alienation over thunderous drums and percussion, layers and layers of sludgy guitars and samples from horror films, was the fact, Taylor says, that they meant it.

"We weren't just singing about Satan or trying to be shocking for the sake of it," he says. "We really were that angry, we were shocking because we were coming out of the gate so steeped in guttural anger. And we found all the kids who felt the same and they related to us."

The fear was widespread. When the band's second album Iowa was released, just a week before the New York 9/11 attacks in 2001, US censors banned Slipknot, along with the likes of System Of A Down, Rage Against The Machine and Marilyn Manson from radio and TV.

But Slipknot weathered the storm. They no longer seem as shocking and their record sales now total almost 25 million. Their sound, as well as their carefully cultivated and maintained image, has grown and developed, too. The band's masks and stylistic themes, for example, change with every album.

"If we were just a band with an image, we'd not be as hot today," says Taylor, 41. "We hit on so many different cylinders. It's the real thing. We have the look, we have the artwork, we have the songs, and the songs are what keep you there. We've been able to continue to write really, really well.

"We've written great hooks, great melodies, abrasive, aggressive music, and that's what scared the parents so much - the masks weren't just gimmicks to sell music, and the anger was real."

It was here in the UK that Slipknot were first embraced, and as a result, Taylor says it's still his favourite place to play.

"The UK was the first place that believed in us, and we've never forgotten that. I remember the first time we came over in 1999, each time since has been bigger and better, and now we come back and it feels like a homecoming, whether it's for our tour or for a festival like Download. We're so lucky."

This time around, Slipknot are touring on their Prepare For Hell shows with metal bands Korn and King 810, and just as they did during their shows in the States late last year, they have three different set lists in circulation - to ensure that any hardcore fans who go to multiple shows will likely see a different gig each time.

Taylor says they'll be playing songs from each of their five albums, and there'll be a mix of heavy anthems, sing-alongs and some surprises too. "It still shocks me that a band like this can have a sing-along, but there we are."

Their most-recent album, .5: The Gray Chapter, was released last September, and found the band going back to the kind of brutal guitar music of their second album, Iowa.

While Taylor says it would've been easy to play only their heaviest catalogue songs to blend in with the new material, he's conscious of alienating any of their fan base.

There's also the possibility that playing too many songs from the album could be too upsetting. It is, after all, a tribute to founding member Paul Gray, who died of an overdose of morphine and fentanyl in 2010.

The album was always going to be a tribute to him, Taylor notes, and the reason it took so long after his death to come out was down to taking time to work out what the message would be.

"Fans have had issues with me because they felt it was my fault we've been away for so long, but we didn't want to run right in and make anything that felt forced, we wanted to wait to make an album," he adds. "We wanted to reach the point where we knew what we wanted to say, and how we wanted to say it. It took all of us in the band time to get on the same page with the message. I don't know about the others, but if it took another six years to get there, I'd have waited.

"And maybe the reason it took so long was that it's basically letting go of the grieving process," he continues. "That grieving connects us to Paul, and maybe we didn't want to let go of that feeling. But we needed to. Perhaps some of the aggression and feeling on the album comes from there.

"We needed to stop feeling that depression and get back to the positive stuff we remember about Paul. And we did, while making the album.

"Once we did that, I felt 20 times lighter. Making this album was really important."

He recounts the band's first post-Gray performance at Sonisphere Festival in Athens, Greece, in 2011, and feeling like he was performing inside a bubble, unable to hear the fans or remember anything about the first four songs.

"And then the fans reached in and brought us up to where we needed to be. Before that, we weren't sure if we were able to carry on without Paul, but that show, and the fans, made us realise it was possible.

"So The Gray Chapter is telling a story," he concludes. "It's about letting the fans know we've been knocked down, and it's about sharing - it's not preaching our grief, but sharing it, and letting them know where we've been the past four years.

"Sometimes it's scary to get this real with people, but the catharsis is amazing. There is still some stuff that's hard to talk about, or that I won't talk about - private stuff about our friendship - and fans have a hard time with that, but I have to keep some stuff back for me. I don't have anything left unless I do that."

EXTRA TIME - FIVE MORE MASKED BANDS

:: Insane Clown Posse - ICP's face paint is so iconic its spawned its own subculture, the Juggalos, who have their own practices, slang and annual gathering.

:: Mushroomhead - These metallers formed in Cleveland, Ohio, in 1993. They feuded with Slipknot for some time, saying they'd copied their look, but have since buried the hatchet.

:: Pussy Riot - The Russian protest singers, who became famous when three members were arrested and jailed sparking global uproar, wore masks more for their own protection, as they sang anti-Putin songs.

:: Gwar - A thrash metal band from Virginia, their grotesque costumes are based around sci-fi mythology, which depicts the band as alien warriors.

:: MF Doom - The villainous alter-ego of rapper Daniel Dumile wears a metal mask on stage, but he's sometimes been criticised and accused of getting imposters to perform on his behalf.

:: Slipknot's fifth album .5: The Gray Chapter is out now. For tour dates and locations, visit www.slipknot1.com