You only have to open a style mag, left-field music publication or a broadsheet at the moment to see that heavy metal is enjoying one of its many periods of critical rehabilitation. But like a great comet that appears in the night sky once every several centuries, it will soon disappear from the mainstream again, becoming once again the last true youth tribe left after the homogenizing effect of the 90s, standing alone in splendid isolation. If there is one behemoth of a metal band that will not be affected by the vagaries of style – either way – it is Judas Priest. It doesn’t matter how much people claim that metal is an influence on the cat walks and put on doom metal shows in art galleries: Judas Priest will remain potentially the most un-trendy, the least co-opted band ever formed.

To the public at large they will always remain a mystery; an anachronism; an embarrassment. To their legions of fans, they will always be the innovators; the unswerving one-percenters; purveyors of REAL METAL. Whatever your take on them musically though, one thing is undeniable, they are one of the most important and innovative heavy rock bands ever. They bridged the gap between the heavy metal mark I of Black Sabbath and the myriad genres of the 80s and beyond. They basically laid the bedrock for thrash, death, black and other forms of metal madness that would save it from being just another offshoot of rock and help it become the most dominant musical genre of the last two decades. There was also a dark side to Judas Priest that was never very far away and, intended or not, they were – and still are – dogged by controversy that was a million miles away from the throwaway daftness of their involvement with Hear 'n Aid or the video to 'Breaking The Law'.

In 1990, for example, just before Halford took a 12-year break from being in the band, they were unsuccessfully sued after it was alleged that a subliminal message ("do it") contained in 'Better By You, Better Than Me' caused two young men to shoot themselves in the head with a shotgun. When we meet Rob Halford today rather than a straight forward God of Metal, he seems to be some sort of supernatural being of empathy. Within minutes of talking to him, he's given me a genuinely heart warming message to pass on to a young gay metal fan who is being bullied at school and starts showing genuine concern about the fact the author has stopped drinking. There may be a popular perception of these elder statesmen of rock as being uber-pampered children who resemble a cross between Gary Bloke out of Private Eye's ‘Celeb’ strip and a character from Spinal Tap. Of course, the truth, as always, is anything but. Halford – one of the equal, if not the, most important figures in heavy metal – doesn't need to act the big I am in front of mere hacks and members of the public. He isn't some Herbert from a two bit indie band who's had loads of smoke blown up his arse in Camden or Williamsburg. He doesn't need to prove himself.

He’s disarmingly frank about his sexuality, acknowledging that pretty much no one followed his lead in outing themselves amongst metal musicians and that it upsets him to hear about young gay people getting bullied: "If you could tell that lad that I understand what he's going through and he's not alone. I've become something of a figure head in metal for all the gay metalheads and it's something that I take very seriously. He should be able to go on the internet; there are some networking things that are there or hopefully find a friend who you can talk to when you need to. That's it though, look it's 2008 and there's this young metalhead guy and he's going through exactly what I went through when I was a teenager and coming to terms with myself. It's a very difficult, painful, lonely experience and you feel like a freak and you ain't. You're not a freak, you're perfectly normal – you're ok. But you feel so isolated that in some instances it can be very dangerous. So it's important for him to understand that he's not alone and the people who pick on him are a bunch of twats. They're just stupid and fucking ignorant. So he should do whatever he needs to do to look after himself."

As for the drinking, he has the full disclosure attitude of someone who is an old hand at the 12 steps: “I stopped drinking on January 6, 1986 and I haven't had a drop of booze since. It was the best thing I ever did for myself.

“I had my denial thing, you know 'Oh, I haven't got a drinking problem' but I tried to mask it all by saying 'I won't have a drink before 6 O'Clock and I'd have my eye on the clock waiting for 6 and as soon as it came I would start drinking and then I would drink until I fell over and had to go to bed.”

He says he was lucky to have people round him who whisked him off to a drying out clinic in Arizona, and thanks to the programme he was placed on, he hasn’t supped since: “I remember the first ever show I did sober with Priest at the Tingley Coliseum in Albuquerque, New Mexico and that was in 1986. It was the first date on the Turbo tour and it was the first time I'd walked on stage without having quite a few drinks under my belt. Before I would have had three or four vodka and tonics or whatever and I'd have a bit of a buzz before I even got on stage. But for the first time I went on stage clean and sober and I had the best show of my life because the music had suddenly become my drug. The music was giving me all the things I hadn't realised it was giving me because I was pissing all over it with booze and drugs. But you can do it. I've got loads of mates out there who drink; everybody in Priest drinks but it doesn't affect me. I certainly steer clear of the temptation because I'm a recovering alcoholic and there aren't any other alcoholics in Priest. So when they want to have a drink they have a drink but with me I'd have to have a drink to get pissed and everything else."

It has been well documented how Rob's band changed the entire sound of heavy metal but less commented upon is the fact that they pretty much invented the uniform as well. Much maligned or not, Priest were almost single handedly responsible for creating and cementing the uniform of studs, leather and denim. Remember, before Priest, metal bands were pretty much just hippies. He agrees: “Yeah, and we respect being acknowledged in that way as well. When we started we had the sound going on but the look wasn't all there. And so when we finally got round to putting all the leather on and all that we thought 'Yeah, it's looking like it's sounding.' We were one of the first groups to really push that type of image and we had no idea how much of an influence that was going to be but it certainly turned out to be something that did that. If you see someone walking down the street, dressed a certain way and you say, 'Yeah, they're a metalhead'. And it's the same if a metal band taking the stage. They're a metal band and they've got the look. It makes us part of what we call the metal community.”

Dress down Friday for Judas Priest

The more you talk to the guy, the more you realise that the Halford of 2009 is probably not all that different to the Halford of 1969. Except now he’s dressed head to toe in black leather and metal studs. He has retained his plumy Walsall twang and doesn’t seem to have any of those daft trans-Atlantic rawk affectations that Spinal Tap parodied so well. He's obviously proud of his roots and has a complex relationship with the West Midlands: "We always said that part of the reason why we got into music, after the chance to play together and have a great time, was to escape. It was to get out of the area that you're from. And that's not in a bad way but it's having a dream – trying to see where your music will take you. As it was Birmingham, particularly in the 60s was a bit of a revolutionary city because there were all these new concrete and steel buildings that were going up. You had a motorway that went through the city so no one even bothered getting off the motorway to have a look. This was the roots of it all. The working class area, the mines, the iron factories, the heavy engineering, that's a great part of the history of Brum. Much like a lot of industrial towns, not just in the UK but in many parts of the world, if you grew up there your dad worked in the coal mine or the factory and that's probably where you were going to end up after school. So for some people it was a case of 'Well, that doesn't really appeal to me so what else can I find to do?' As it turned out for us in Priest in the early 70s that slowly led us out of that type of situation and it has been a long journey, closing in on 40 years now. But I don't know what it is.

Talking of the upcoming 40th anniversary, are there any plans to celebrate that in any way? "Well, we're celebrating today because we got two grammy nominations so we're absolutely chuffed about that. Not just for Priest but for British metal. I don't know what we'll do you know? It's going to be great coming home and doing the UK tour with Megadeth and Testament. That's going to be fantastic. Later on next year we want to do the Nostradamus show, doing all of that in its entirety. So it's already got a lot of celebration lined up for next year [2009] before we even play a note so to speak.

You've got some heavy weight support there. Some people would say that Dave Mustaine of Megadeth is one of the (if not the) greatest metal guitarists of all time. What attracted you to having such an interesting bill? "It was the fact that they're both very special in their own way and very good at playing their own type of metal. We're all totally different to each other and if you come and see that show you're going to get three brands of metal and you're going to see something special from each act. That's what we've tried to do on this Priest Feast. A broad display of different styles."

Talking of Nostradamus, it's an astoundingly ambitious piece of work – symphonic, orchestral, progressive. Loved in some quarters, hated in others. Are you glad that you took a gamble on something so ambitious when other bands may have been tempted to stick to the formula? "Well, I don't think we thought it was a gamble. I think we were just excited about finally getting round to doing something and we had wanted to do it for ages. Because of our ongoing ritual of writing, recording and going on world tours it took forever to get round to having enough time to do it because it was a two year project. And also to find the right subject matter. And then finally Nostradamus appeared and we had all the goods for making it a good record. So really we did it for ourselves. We'd wanted to do it for ages and we finally made it happen. The overall reaction has been solid and sure, it's been mixed in some quarters – some metal heads just want to see Painkiller, Painkiller, Painkiller or British Steel, British Steel, British Steel but that's not what being in a band is about, especially not for us. We want to see what we can do. This is a fantastic time for Priest and our fans and we're still enjoying going through the opening stages of introducing the music of what will become a fully fledged stage show, playing all of it in concert."

Do all of you feel healthy as a band? Can you see yourself doing this indefinitely? "Well, you have to be practical. We're not getting any younger but it's not slowing us down. The energy and excitement are still there. We still love playing together as a band. We're good mates. We know that we can write good music. The team of writers is very strong as everyone has just experienced with Nostradamus. We have a will and a determination. If and when we decide it's over it's not going to be broadcast, we're not going to say we're knocking it on the head. We'll probably just . . . fade away (burst out laughing). But we're not fading yet we're bright and shining in the metal sky! (more laughter)"

Are you still writing new material now? "We're not one of those bands who can write new material on the road. We finish a tour, we have a rest and then we get together and we start noodling away and making new metal songs."

When you finish this touring cycle - because you've been invigorated by this new, longer, more orchestral direction you've been heading in – do you think you're going to do another album like Nostradamus? "Speaking personally, no, I think we've done it and some things you can only do once and I don't know what we're going to do next but it will be another Judas Priest metal record but it's an exciting thought to know that something's going to be on the horizon."

But his association with the classic bands and history of heavy rock and metal is something that he is audibly proud of as he recalls the day that Priest opened for Zeppelin in Oakland, San Francisco, 1977: “It was a bitter sweet moment for me because those were the last shows that [drummer, John] Bonham did. But you can't forget something like that, it's a vivid memory. Going on stage as we did early in the morning because there was a 4pm curfew in the afternoon, we were on stage and the stage was still full of the fog that rolls in from the Bay and you could really see the whole of the stadium at first but as the sun came up and burnt all the fog off you could see 80,000 people there at 10am in the morning which was mind blowing. And those were two shows back to back. 160,000 in two days. That really helped to break Priest on the West Coast of America. Besides that just hanging around seeing Zeppelin playing with that line-up was mind blowing. It did your head in how good they were.”

And you know that long after the fly-by-nights have passed on again and the fashion mags have found another genre to dally in, Halford will still be in the middle of the metal firmament; constant and unmovable.

This is an edited extract of an interview with Judas Priest from the current issue of The Stool Pigeon newspaper. Also in the February edition: Mastodon, Franz Ferdinand, PJ Harvey and John Parrish, Darren Hayman, The Damned, M Ward, Dan Deacon, Grandmaster Flash and more. For a list of stockists, visit the Stool Pigeon website.