When Rob Reiner's comedy This is Spinal Tap was released in 1984, in effect creating the mockumentary genre with its tale of a deluded English heavy metal band's dismal American tour, many people thought it was a true story. When Anvil! The Story of Anvil, a documentary that features a Canadian heavy metal band's dismal European tour, began screening at film festivals in 2008, audiences were certain it was a mockumentary. It was just too good, or perhaps too bad, to be true.

But Anvil! The Story of Anvil, which opened nationally yesterday, is all too painfully, and eventually triumphantly, real. Even Anvil's drummer, Robb Reiner (whose name many felt was a clue to the film's fictional status as a Spinal Tap tribute), was shocked when he saw the final edit by debutant English filmmaker Sacha Gervasi.

"When I first saw it I was blown away," Reiner recalls. "I had to watch it three times in a row just to make sense of what I was witnessing. I liked it but it caught me off guard."

Reiner and his best friend of four decades, Anvil's frontman Steve "Lips" Kudlow, were in Melbourne two weeks ago to promote the movie, alongside Gervasi and Australian-born producer Rebecca Yeldham (The Kite Runner). Fittingly, for a band that recently opened for hard rock titans AC/DC, they did their interviews at Cherry Bar on AC/DC Lane in the city. A weekend preview screening at Carlton's Cinema Nova saw the duo receive a standing ovation when they walked on-stage for the post-screening Q&A session.

"The film has exceeded my expectations and they were very high," explains Gervasi, who was a teenage roadie for Anvil - who affectionately nicknamed him "Teabag" because of his nationality - in the mid-1980s.

"It's become something quite magical. People love this film and it's relaunched Anvil's career."

The praise for Anvil! is close to universal. Ozzy Osbourne claims to have already watched it seven times, while actors as diverse as Dustin Hoffman and Tilda Swinton have raved to Gervasi. French filmmaker Michel Gondry (Eternal Sunshine of the Spotless Mind) told him it was his favourite film of 2009 and Keanu Reeves was proudly photographed with Reiner and Kudlow.

But until Gervasi rediscovered them, Anvil appeared set to be nothing more than a footnote in the history of rock music. Founded in Toronto in 1973 by then 14-year-olds Reiner and Kudlow, the group released a trio of moderately successful albums between 1981 and 1983 that influenced the subsequent generation of heavy metal heroes. Anvil! opens with the likes of Metallica drummer Lars Ulrich eulogising the band, even though they had resolutely carried on as middle-aged musos with menial jobs and obscurity beckoned.

The barrel-chested, taciturn Reiner and the diminutive, optimistic Kudlow (the "Lips" are still prominent) are adamant Anvil would have kept playing no matter what but the movie makes clear they were near to the end in a professional sense - a disastrous run of gigs in Eastern Europe culminates in them headlining a festival in Romania where the expected crowd of 20,000 is, in fact, 174.

But at a certain point, courtesy of 320 hours of footage shot between 2005 and 2007, the focus moves from Anvil's misadventures to the bond between Kudlow and Reiner.

"Knowing how hilarious Lips and Rob are, as well as being exceptional people who defy the stereotypes somewhat, I had an idea that if we got their lives in the film, people would laugh at the beginning and then be genuinely involved as the layers were peeled away," says Gervasi, a King's College history graduate and journalist who reinvented himself as a successful Hollywood screenwriter when he penned The Terminal for director Steven Spielberg in 2004 (he was also recently an uncredited screenwriter on Transformers: Revenge of the Fallen, an experience that gave him a raft of amusing anecdotes he only tells off the record).

"This movie is about human values. We all have friends for life, we all have a family," Kudlow explains. "What makes this movie so spectacular isn't that it's about a heavy metal band, it's the emotion and the human aspect of life."

Gervasi and his crew had no problem catching deeply amusing moments, be it Reiner talking about a drum solo that he calls "White Rhino" or a Prague club owner being so annoyed at the band getting lost and being hours late to a gig that he pays them in bowls of goulash.

But the band isn't sure if the director was able to fully divorce himself from their mounting, and increasingly despairing, misfortune. "He would deny that he got involved but he did," Kudlow insists.

"I did feel it but I had a job to do as a filmmaker," Gervasi says. "I had to be a fan, a friend and a filmmaker. The worse it got for them, the worse I would feel personally but I'd also be delighted as a director. It was an up and down experience."

And even though Anvil remain one of Gervasi's favourite bands (he himself went on to play drums and in the early 1990s was a member of an early version of the multi-platinum band Bush), he cannily kept the focus in the movie on the personal dynamic as opposed to the music. Anvil are rarely seen playing for that long during Anvil!

That's now changing. While the singer and drummer have diligently promoted the movie, the focus is now swinging back to their music career. This is Thirteen, an album the documentary shows being funded by Kudlow's sister (they've since repaid her), is out locally today, their first release here since 1983.

They also have professional management and a solid touring schedule, which includes Australia in February as part of the Soundwave Festival at the Showgrounds.

"Everything that's happening is completely appreciated on a level that's 100 per cent greater than you might do if you were 25 years old," Kudlow enthuses. "At this point in my life, having worked long and hard, the success in my career is happening at a perfect time. We have a huge back catalogue and a genuine legacy now."

Reiner adds, venturing a brief smile: "We've been working hard because this is what we always wanted.

"We're finally living the dream."

Anvil! The Story of Anvil is now screening.

-Craig Mathieson