Not since Spinal Taphas a rockumentary caused such a kerfuffle.  Anvil! The Story of Anvilhomes in on the Canadian metal men as they attempt to turn the dial back up to 11.  Donald Clarketalks to director Sacha Gervasi as well as its heavy metal heroes Lipes and Robb

THERE is no escaping Spinal Tap. Anvil, Canada's loudest band, have just flown in from London and they are feeling a bit peckish. Robb Reiner, the band's drummer, scrutinises the menu.

"Erm. What's the fish of the day?" "It's probably some kind of white fish," Sacha Gervasi says. "Like cod or herring?" "Plaice maybe." What was it Nigel Tufnel said? "In the US you have cod. I like cod. And I love tuna. Those little cans you've got here, tuna fish." Gervasi has just directed a magnificent documentary about Anvil and many viewers – even those who haven't heard the band discussing fish – have drawn comparisons with Rob Reiner's (one "B", mind) classic This is Spinal Tap.

But Anvil! The Story of Anvilis a more compassionate work than such comparisons imply. True, the picture does detail embarrassing incidents in the career of an ageing heavy-metal outfit. Over the first half hour we follow Reiner and Steve "Lips" Kudlow, the band's original guitarist and singer, as they attempt to get by in contemporary Toronto. Thirty years after they formed the band, the two men are now forced to work odd jobs to keep themselves in loo roll and plectrums. Then an opportunity arises to embark on a European tour. Inevitably they miss too many trains, get lost in too many capital cities and allow themselves to be mismanaged by a scatterbrained woman with blonde hair.

Yet, as the film progresses, the two guys emerge as contemporary heroes. Loyal to their decent middle-class families, dedicated to their cacophonous art, Reiner and Lips ultimately come across like brighter, more optimistic versions of Mickey Rourke's character in The Wrestler. It's almost as if Gervasi consciously got the Spinal Tapstuff out of the way early on and then set out to investigate the true natures of these likeable men.

"That's absolutely right," the director replies. "Billy Wilder said that a film-maker must grab the audience by the throat right away. So we grab them by the throat by inviting them to laugh their asses off. Look, it's about a band called Anvil who have an anvil on every album cover. One of the guys is actually called Robb Reiner. There was no way, however hard I tried to avoid it, that anyone reviewing the film would fail to mention Spinal Tap. So, we decided to turn that into a strength and give people a false sense of security about what the film is doing."

Gervasi and Anvil make an unlikely team. Lips, hair still flapping like a cocker spaniel’s ears, comes across like a middle-aged child who has just ingested too much tartrazine. Reiner, taller and more lugubrious, would not look out of place waving a sword in the background of a Tolkien adaptation.

Gervasi is, by contrast, every inch the slick media operator. Sharply dressed in a crisp shirt and spotless trousers, he makes a point of pumping your hand, remembering your name and acknowledging the current location: “So, Donald, how do you think this will go down with an Irish audience?”

Yet, for all their apparent cultural differences, Anvil and Gervasi have been pals for a long time. "It all began in 1982," Gervasi explains. "I was a huge fan of metal and I fell in love with Anvil when I saw Lips on the cover of Soundsmagazine. He was just incredible, scary, weird, inappropriate, angry and happy. It was a fantastic image. He was wearing leather, clutching this dildo between his teeth and brandishing a chainsaw."

At this stage, Anvil were on an equal footing with an advancing pack of new metal gods that included the likes of Metallica and Slayer. Gervasi, barely out of public school, went to see the band at Castle Donington and managed to inveigle himself into their entourage.

Nicknamed Tea Bag – because he was English, you see – the young fan found himself sharing the bus with fellow hangers-on such as “Vegas, Spider, Jethro and the Brit”.

"Years later, in 2005, long after we'd drifted apart, I thought: I want to hang out with my old mates," Gervasi says. "I'd wondered what had happened to them. They had this great first album called Metal on Metaland were on the cusp of being huge, but hadn't made it. So, I went on this website and discovered that Anvil had done all these albums I'd never heard of. They were still playing live. So, I phoned them up and Robb came up with this great line: 'Hey, Tea Bag. We thought you'd died or become a lawyer.'"

As it happened, Tea Bag had spent the previous 20 years developing a successful career in Hollywood. Having written The Terminalfor Steven Spielberg, Gervasi had access to any number of distinguished producers and financiers. He phoned Steve Zaillian, writer of Schindler's List, and told him he had a great idea for a documentary. Zaillian met Lips and agreed that he was the sort of extraordinary character about whom great documentaries are made.

“It’s weird,” Lips says. “I mean you always take yourself for granted. I thought: I am just myself. What are these guys talking about?” Did no alarm bells ring? Gervasi could have made the guys look quite ridiculous. “Absolutely not. We never mistrusted the project for a second,” Lips says. “What good would it do to make a film that made the band look bad? What would be gained? He’s our buddy.”

Sure enough, although the resulting film is often hilarious, it always permits the band members their dignity. It’s been a hard life in many ways. The opening footage includes encomiums from the likes of Motörhead’s Lemmy and footage of the band playing massive festivals in the early 1980s, before going on to show Lips carrying out his delivery job for Choice Children’s Catering.

What went wrong? Why did Metallica become gods and Anvil become van drivers?

“There was nothing wrong with the music,” Reiner says. “We just didn’t have the right people working for us. We were very much ahead of the curve in terms of what was to come with speed metal and so on.”

As ever, Gervasi offers further positive spin. “They had a rock manager who had managed AC/DC, the Scorpions and Bon Jovi,” he explains. “But speed metal just wasn’t part of that equation. He didn’t get it. It wasn’t until Metallica came along that he eventually got it. Can you believe it? He didn’t want them to play 666. That is their key song.” He didn’t want them to play 666? With lyrics like: “Hitler and Manson were my right hand! To these men I entrusted my sacred laws!” The man must have been crazy.

At any rate, it looks as if the Anvil story might end up having a happy ending. Following good early buzz at the London Film Festival and Galway Film Fleadh, the documentary played to ecstatic acclaim at this year’s Sundance Film Festival. Two weeks ago, Anvil played a gig after a screening at the Jameson Dublin International Film Festival and the picture won the festival’s audience prize.

“Sundance [Film Festival] was incredible,” Gervasi agrees. “We had to show it to a test audience of about 600 people and we had no idea how it would go. There was an eruption. There was a standing ovation and it’s been like that pretty much ever since.”

“Yeah, we walked away knowing we had caught a kind of magic,” Reiner says. “We had thought there was something there and that confirmed it.”

Gervasi goes on to point out that the story of the film continues after the credits have rolled. If you want to know the sequel, just check out the website to see where Anvil are playing next. When The Story of Anvilcloses the band have recorded a new album, This is Thirteen, and are preparing to play a gig in Japan. Has the film's growing reputation helped sales of This is Thirteen? "Oh yeah. We have a real manager now and a real agent now," Reiner says.

“People are buying the album and we have been booked into Glastonbury. There is this awareness spreading that we are still here. And now it’s happening at a better time for us.”

“Overnight success you tend to take for granted,” Lips agrees. “We have worked so hard. This new success comes with real appreciation. We get what it means this time. We get what an amazing miracle this is. Nobody is losing it this time.”

Among the many things that make the two men so likeable is their unwillingness to whinge or to admit serious regrets. Yet, there must have been times when they considered throwing it all in and going back to college. Twenty years is a long time to hang on to a dream.

“No. This is what we do. This is who we are,” Lips says with uncharacteristic aggression. “We do other jobs to support this. That’s how it works. When you do something the best that you can, than that thing becomes who you are.”

But it must have been hard on their families. Both guys come from sensible Jewish backgrounds and, although the mums, dads and siblings have been largely supportive, solidarity is seen to briefly break down in the film. At one stage, Reiner’s sister declares that the band should accept that “it’s over”.

“Well that’s my sister and she has her own issues,” Reiner grumbles. “I don’t really want to go there. My wife and family are rock’n’roll people. My son is in a band. My wife has been with me my whole career. She is supportive. This life is her life. She’d kill me if I left.”

And he never lost faith? “Never. All I ever wanted to do was rock. I’ve been dealing with this stuff for 20 years and I always knew we would be discovered. I always knew.”

Anvil! The Story of Anvil is released today

Spice boy: the Sacha Gervasi story

Anvil! The Story of Anvilends with a snap of the director taken in the early 1980s. Who is this man? Some anonymous metal fan who struck lucky a quarter of a century later? Not quite. Sacha Gervasi is, in fact, the sort of ubiquitous, polymathic, well-connected, but still slightly mysterious figure you might find appearing every 30 pages in a novel by Evelyn Waugh or Anthony Powell.

The son of an economic adviser to president John F Kennedy, the grandson of a famous foreign correspondent, he attended Westminster School (alma mater of John Gielgud, Tony Benn and Shane McGowan), before studying history at King's College, London.

Following his early adventures with Anvil, he "almost died from a drug overdose and briefly studied to be a lawyer". He worked for a spell as secretary to Ted Hughes, then poet laureate, and, in the late 1980s, somehow found himself arranging a sale of Samuel Beckett's personal papers at Sotheby's.

Having tried everything else the universe had to offer, he headed for Hollywood in 1995 and, following a successful spell at UCLA film school, managed to get two scripts into production. The first, The Big Tease, was not a success, but the second, The Terminal, saw him working with Steven Spielberg. He is now in constant demand as a script doctor.

"I ended up sucking on the big studio teat," he says. "I still do that. I love doing that. But that's the day job."

What else could Gervasi do to further flesh out his extraordinary backstory? Well, he could, perhaps, father the child of a Spice Girl. In 2006, Bluebell Madonna Halliwell, daughter of Geri Halliwell and our hero, entered the world. Even Waugh would have trouble making that up.