In a raft of glowing reviews, there have been no end of adjectives used to describe Rocketman – but “down-to-earth” isn’t one. According to its star Taron Egerton, the Elton John movie is a "fantasy", not a factual biopic. It’s just as much of a glamorous confection as his songs, and anyone looking for authenticity – for the man behind the oversized glasses – should look elsewhere. But where?

Try a low-fi rockumentary called Tantrums and Tiaras. Shot on a shoestring budget in 1995, and running to just 75 minutes, this fly-on-the-wall film captures his every quirk with rare intimacy. It's not easy to get hold of: at the time of writing, there's only one copy of the DVD on Amazon, implausibly priced at £77.46. But it's worth hunting down. It is a warts-and-all portrait of Elton John’s soul – raw, revealing and extremely funny.

The tantrums of the title come thick and fast. Just two minutes in, we find John in his dressing room, about to film a video to promote his single Believe. He’s not entirely happy about it. “I make music, I don’t make f---ing films!” he snaps to the assistants hovering nearby. “I hate f---ing videos, they’re f---ing loathsome. And I tell you this: I am not doing this video.” (He did, of course.) He is never short of opinions. “People who take flower-arranging classes,” he asserts, “should be shot.”

If Tantrums and Tiaras has the feel of a home movie, that’s because it is. It was the first film directed by John’s now-husband David Furnish, who followed the singer through every step of his 1995 world tour, just a year and a half after the couple first met. At the time, he was Britain's highest-earning musician, constantly surrounded by the barrier of his entourage. Furnish captured personal moments no one else could: when speaking to the man he loves, the star lets his guard down. In one scene, he admits the reason music videos make him so tetchy is his insecurity about his looks. “I’m not Madonna, I’m not George Michael…”

We meet John’s mother, who bursts into tears remembering his drug abuse, and proudly reads his music teacher’s report from 1963: “I was very pleased that he passed his grade seven with merit... However, I am most concerned about him as he is now 16 and yet he still behaves like a child of 13 or 14, with fanciful notions of becoming a star and rocking and rolling all the time.”

Taron Egerton as Elton John in Rocketman credit: AP

His unflappable grandmother, meanwhile, emerges as a quiet anchor in the singer's life. “When I was in Los Angeles, and tried to commit suicide by taking sleeping tablets and throwing myself in the pool, [I was with] my grandmother who was on her first trip to America,” John recalls. “I said, ‘I’ll be dead in two hours,’ and she said, ‘Oh, I suppose I’d better go home then.’” His devotion to her is clear in a scene when he visits her in her retirement home; it turns out to be their final meeting before her death.

It’s not all personal drama. There is also plenty to interest fans looking for an insight into how he writes his hits. How long does it take to come up with a melody? “Never usually more than an hour,” he says. “If it doesn’t come to me within an hour, I abandon it.” We see this in action; in the studio he conjures up a tune from a sheet of Bernie Taupin’s lyrics, then turns it into a duet with Sixties icon Lulu. It’s brilliant, but was apparently never released; this documentary is the only place to hear it.

Inside the rock diva is a shrewd businessman. John is obsessed with quantifying his success; he carefully updates a colour-coded diary of his sales in America and Britain, and says that following the charts is “the most exciting part of having a record come out”. He is clearly a workaholic. In one quietly touching scene, Furnish finds him poring over his paperwork late in the evening and asks, “Don’t you think you should take a rest – a proper rest?”

Elton John performing in California on his 1995 world tour credit: Getty Images

But for the star, relaxing isn’t as easy as it sounds, as we learn when he takes a holiday in France. The rocket man does not travel light. He brings a small pharmacy of vitamin bottles, a freezerful of M&S muffins, and a wardrobe large enough to clothe an army of Elton John impersonators (with two large wooden chests of drawers just for his glasses), as well as what Furnish calls their “medieval court” of followers and assistants.

“Are you afraid of being alone on holiday?” Furnish asks. “Could you go on holiday and not have a driver, not have a valet and not have a tennis coach?” John thinks for a moment: “Probably, but I wouldn’t enjoy it very much.”

Tennis practice inspires another tantrum. John is distracted from his game by a waving fan, so hurls his racket across the court and storms off. “I’m supposed to be on holiday!” he moans. “I’ll never come to the South of France again!” Back in the hotel room, he orders his staff to book him a plane home immediately. (He doesn’t take it.)

“He is a totally obsessive compulsive person,” his therapist Beechy Colclough tells Furnish. “If it hadn’t been the alcohol, it would have been the drugs. If it hadn’t been the drugs, it would have been the food. If it hadn’t been the food, it would have been relationships. If it hadn’t been the relationships, it would have been the shopping. And you know what? I think he’s got all five.”

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What’s remarkable is that – despite all the above – John comes across as immensely likeable and self-aware. Reflecting on the furore around the film six months after its broadcast, he said: "Some of the press said it was like [Coronation Street character] Bette Lynch storming around with a leopard skin coat on – which was a very accurate description."

From the outset, he encouraged Furnish to include all the messy parts of his life. “I don’t want the documentary to come across as holier than thou,” John tells him in an early scene. “I don’t want a sycophantic one. I just want people to see me as I am.” When so many of today's pop stars strive for Instagram-perfection, the frankness and humour on show in Tantrums and Tiaras remain an absolute tonic.