Danny Boyle is up and running again. The man who gave us the euphoric highs and gutter lows of Trainspotting, with Iggy Pop lusting for life as Ewan McGregor pounded down Princes Street, who gave the zombie movie a jolt of adrenaline in 28 Days Later and tried to set fire to the stars in the sci-fi thriller Sunshine, might just have a monster hit on his hands with his latest, Slumdog Millionaire, a tale of an 18-year-old orphan from the Mumbai slums who reaches the final of Who Wants to Be a Millionaire? This is an improbable story in every way, touching on tectonic cultural and economic shifts, the unwieldy apparatus of the movie business, the mysterious, alchemical nature of audience response and the latest reversal of fortune in a directorial career that is proving as predictable as next week’s stock prices.

As recently as August, it looked as if Slumdog Millionaire would go undistributed in North America. A little movie about Indian slum children, with subtitles and no stars, didn’t seem like a natural fit in cinemas dominated by the Dark Knight and Harry Potter. Boyle’s name probably wasn’t much of an inducement, either. The excitement that surrounded Shallow Grave and Trainspotting has long since dissipated after the back-to-back flops A Life Less Ordinary and The Beach. Although 28 Days Later was a cult hit, Boyle has never approached blockbuster status in America and his last film, Sunshine, returned just $4m in the region, on a budget of about $50m.

Produced by Film4 and Pathé in the UK (where it is the closing gala film at the Times BFI London Film Festival on Thursday), Slumdog had significant funding from Warner Independent, the so-called speciality division responsible for lower-budget “prestige” movies such as In the Valley of Elah, The Painted Veil and Infamous.

In May, however, Warner Bros took a look at the numbers and decided it could no longer afford to be in the prestige business, leaving Slumdog in limbo. (At much the same time, Paramount reached the same conclusion and shut down Paramount Vantage, the division that released the Oscar-winning There Will Be Blood and No Country for Old Men last year.)

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BACKGROUND

• A journey from the gutters to the stars

• Boyle explains why Mumbai is a key location

• Urban fairytale wins film awards

• Slumdog Millionaire may become film winner

• The Big Film: Slumdog Millionaire

BACKGROUND

• Slumdog Millionaire: the Indian press reaction

• Fours stars for Slumdog Millionaire

• Slumdog Millionaire - the Sunday Times review

• Slumdog Millionaire

• Slumdog success silences national row

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• Boyle explains why Mumbai is a key location

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In Boyle’s words, “We were dead and buried” — but it wasn’t as over as it felt. Warner allowed Peter Rice at Fox Searchlight to take a look at the film and, in a highly unusual move, the rival studios agreed terms enabling Fox Searchlight to release the picture in North America next month, with a British release planned for January.

Right now, that looks like a smart deal on Fox’s part.

The movie premiered at the upmarket Telluride film festival at the end of August, and critics exhausted their stock of superlatives on it. So much so that when Boyle introduced the film at the Toronto Film Festival a week later, he was already careful to damp down sky-high expectations. He need not have bothered. The sellout Toronto crowd was enraptured (Slumdog won the audience award) and “this year’s Juno” is being touted as a dark horse for the Academy Awards — which would be a first for Boyle.

When we met in Toronto the day after the public screening, he was, as usual, modest and taking nothing for granted. At the same time, he knew the movie had “played” — he would have to have been comatose not to have sensed it. In fact, you could pinpoint the exact moment when the audience fell in love with it. It’s a scene a little over five minutes in. We have already seen 18-year-old Jamal (Dev Patel) in the hot seat of Who Wants to Be a Millionaire?, preparing to answer the last, 20-million-rupee question. We have also, jarringly, seen him brutally beaten and interrogated by a couple of deeply suspicious policemen. How can an illiterate chai boy from the slums have known so many correct answers, they want to know — is he a genius, a cheat or just plain lucky? Thereby hangs an unabashedly romantic and picaresque tale.

In the first flashback accounting for his improbable knowledge, we find the seven-year-old Jamal trapped in a wooden outhouse built on a rickety pier that overlooks a private airport. Desperate to greet his favourite Bollywood star, Jamal realises that there’s only one thing for it. He takes a deep breath and plunges into the stinking cesspool beneath the pier. Covered in crap, he walks up to the star and demands his autograph. The sequence may be shamelessly contrived, but the close correlation between money and excrement speaks volumes about India — and not just India, for that matter.

Boyle, who looks like an overgrown street urchin himself, laughs when I draw the obvious comparison with a similarly placed scene in Trainspotting, in which McGregor dives into the filthiest lav in Scotland to find his drug-filled suppositories. He claims it is a British quirk: “We’re obsessed. At least one in every two British films has a toilet scene. It’s rare in other cultures.”

Slumdog’s screenwriter, Simon “The Full Monty” Beaufoy, who has adapted Vikas Swarup’s bestselling novel Q&A for the film every bit as freely as the inspired title change suggests, confirms the scene was written more than a year before Boyle came on board. “I read the book, then I hung out in Mumbai and wandered around the slums for weeks,” he says. “Those piers are in the Juhu slum. They’re big, long piers with wooden shitters at the end, which are open, and you can sit there and watch the film stars landing at the private airstrip — a grandstand view! I thought I really had to write that in. The scenes just come at you like a train in a place like that.”

The cast was largely local, with 10 personnel brought in from the UK. And with the exception of the slimline Patel, from Channel 4’s Skins, as the teenage Jamal (cast because young Indian actors all work out), Boyle found the kids in Mumbai with the help of a local casting director, Loveleen Tandan, who worked with the younger children and wound up with a co-director credit.

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