‘How did our wee story about junkies become this big?’

One bright May morning in 1996, Irvine Welsh awoke on an inflatable lilo in the middle of a French swimming pool. Bobbing beside him on lilo number two was Noel Gallagher, and lying on the poolside, like some great snake, was a fire hose he vaguely recalled using to blast the Oasis guitarist at some point during the preceding evening.

Beyond that, the previous 12 hours were a blur. They’d begun in Cannes, where the film adaptation of Welsh’s debut novel Trainspotting had its international premiere, and had concluded half an hour’s drive down the coast at the Hôtel du Cap-Eden-Roc, the most elite resort on the Riviera.

Later on, further details would crystallise, including a DJ set by Leftfield at the Palm Beach nightclub, attended by 2,000 revellers including Mick Jagger and Leonardo DiCaprio. But something Welsh recalled immediately was a stray comment from Andrew Macdonald, Trainspotting’s producer, on the red carpet: “We should really do a sequel to this some time.”

Speaking on the phone from his home in Chicago, Welsh explains to me why the idea terrified him. “In Britain we were known for doing quirky little films about this or that,” he says. “But we shy away from doing things like The Godfather, big epics that make massive statements with grand emotional journeys. So I was a bit intimidated, seeing our daft wee story about junkies in Edinburgh as this big thing.”

Welsh, a 59-year-old whose go-to look in publicity photographs could be described as disgruntled bollard, doesn’t strike you as the easily flustered type. His “daft wee story about junkies”, published in 1993, and based to an extent on his own past as a heroin user, made him an overnight literary sensation. He remembers conspiring with his agent to send outraged letters to Scottish newspapers in the hope of drumming up some controversy, “but before I got around to pulling those scams, some early readers had done it for me”.

I have a crisp memory of Trainspotting’s silver-foil cover sliding silently from lap to lap in our Scottish classroom while our oblivious English teacher read aloud from The Great Gatsby, and particularly my friend Chris flicking to a chapter called “Cock Problems” – Mark Renton, who’s played in the film by Ewan McGregor, describing the ups and downs of injecting contraband opioids into his genitalia – and relaying its contents with hotly whispered glee.

When you’re 13, that kind of thing stays with you. But for its author, Trainspotting’s addicts, thugs and drifters also proved hard to shake. They turned up unbidden in Welsh’s head as he wrote Porno, a 2002 novel about the home-brew adult video scene that became a Trainspotting follow-up, and again when he salvaged 100,000 words of unpublished early scribblings from old floppy discs, which provided the building blocks for Skagboys, his 2012 prequel. His most recent book, The Blade Artist, catches up with Francis Begbie, the wiry psychopath played in the original Trainspotting by Robert Carlyle.

And also, for that matter, in the new one. Almost 21 full years after Welsh woke up on that lilo, Trainspotting 2 is here. Though it arrives in cinemas in a couple of weeks, the details of the sequel – lumpily titled T2 Trainspotting – are hard to come by.

At the time of writing, Danny Boyle, who returns as director, is still adding the finishing touches. The nature and extent of Welsh’s involvement is likewise hard to pin down. He spent much of the shoot on location in Edinburgh with Boyle, but the screenplay is credited to John Hodge, a longtime Boyle collaborator who also scripted (and won a Bafta for) the original film.

“I tried not to get in the way too much,” Welsh says. “When they call you an executive producer and give you a lot of money, you wonder if they’re paying you off or saying, ‘Come in and do something.’”

That’s changed wildly in the 10 years since Boyle first broached making the new film, which was initially planned as a by-thenumbers Porno adaptation. Almost as soon as the book was published in 2002, Boyle asked Hodge to write a screenplay, and the duo met Welsh and Macdonald to talk it over. None of them was enamoured with the result.

Problem one (the clue’s in the title): Porno entailed pornography – lots of it – which made a screen version inherently tricky. “Boogie Nights made a success of it, but it’s the exception,” says Welsh, “and the gonzo porn scene was on the way out anyway.”

Problem two: it would be a movie about making a movie, a genre Welsh is “not mad keen on”.

And of course problem three: a number of fallings-out between the

Irvine Welsh tells Robbie Collin how it took 20 years to make a sequel to the film of his book, ‘Trainspotting’ – and why T2 is better than the original