We’re all still workin’ on a Sex Farm

If you're good you'll get these immediately: what is the link between Metallica's 1991 Black Album, the members of U2 getting stuck inside a massive lemon at a gig in Oslo during the Popmart tour, and Ricky Gervais's TV show The Office ? Answer: all were predicted 30 years ago by the best music film of all time, This Is Spinal Tap .

Metallica's Black Album was "a homage", they say, to Spinal Tap's Smell the Glove . When U2 got stuck in their giant Lemon, they unwillingly mimicked a scene from the film. And there would be no The Office if This Is Spinal Tap hadn't pioneered the mock-documentary style.

There are more parallels with real life. You can now buy amplifiers that go up to 11. You can see life imitating Spinal Tap art in the Anvil documentary. You can witness exploding drummer syndrome in real bands. The Tap had only four drummers; Megadeth have had seven and Slayer six.

When Sex Farm, the Tap's classic single, flopped everywhere but Japan, where it reached No 5 in the singles chart, the euphemism "big in Japan" was created for rock bands.

The Tap released a song called Big Bottom , which featured three guitarists playing "lead bass". In 2005, the bass players of Joy Division, The Smiths and The Stone Roses joined forces for a group called Freebass.

In the film, band members talk about composing a musical based on the life of Jack the Ripper, to be called Saucy Jack . "You're a naughty one, Saucy Jack" runs the chorus. Nowadays all rock bands are doing musicals.

It is for its uncanny powers of observation and inspiration that This Is Spinal Tap has been deemed "culturally, historically or aesthetically significant" by the US Library of Congress.

This week, an app is released that features the full version of the film (which no one has ever seen before) and interviews with the rockers it was modelled on. You can get it at the AMC Networks' iPad app "Yeah!" store from now until April 11th. Strictly speaking, it's only available for US users at the moment, but any 12 year-old will help you work around that. I've heard.

This Is Spinal Tap changed how people viewed rock stars. Yes, they really were just as preposterous, clueless and infantile as they were portrayed in the film. It punctured pomposity.

Jimmy Page, Robert Plant, Ozzy Osbourne, Dee Snider and Eddie Van Halen took a while to come around to the fact that it was a parody; to them it seemed like a factual documentary of their musical lives and times. Tom Waits cried when he first saw it, moved by the realism of it all. As did U2's The Edge, who says that "I wept because I recognised so much and so many of those scenes". Smashing Pumpkin Billy Corgan says he once found himself having a heated argument about the deli tray while on tour, just like in the film.

For anybody who pulls on a pair of spandex trousers to go to work, who calls in their legal team when they find the backstage straws aren't of the requested "bendy" variety, or, as Elton John admits to once doing, calls their management team in London to do something about the wind outside the New York hotel suite that is keeping them awake, This Is Spinal Tap is mandatory viewing. Get the app.