Before Trainspotting: Irvine Welsh writes prequel
Trainspotting author Irvine Welsh insists he wrote new novel Skagboys at the same time as his 1993 bestseller.
"Nobody believes me," he said.
The Edinburgh writer insisted the "prequel" was actually written as part of his most famous novel but was not used in the published version.
According to Welsh, when he moved to Chicago three years ago he decided he would either erase his old work or use it in some way.
The 53-year-old writer said he had a fear that he might fall under a bus and leave behind "half-written stuff" which people would publish.
Given the continued interested in the heroin-fuelled exploits of Renton, Sick Boy, Begbie and Spud, he could have a point.
Skagboys takes the characters made famous by Trainspotting and sketches out their lives before the beginning of that novel.
Rather surprisingly it has Renton studying at Aberdeen University before his decline into the world of heroin addiction depicted in the later book and Danny Boyle's 1996 film, starring Ewan McGregor.
Welsh insists it was not difficult to recreate a world he first wrote about almost 20 years ago because the "preamble" already existed.
"I found this initial 100,000 words from the start of Trainspotting that I had never known what to do with and I couldn't throw it away," the author told BBC Scotland's Janice Forsyth programme.
"So I thought if I can't throw it away it must be telling me to do something with it.
"I just went through it and started writing on the basis of what was there, getting inspired by what I was reading and chopping bits out and putting bits in.
"Before I knew it I had another novel on my hands."More reflective
The new book is set in the 1980s - a decade in which Britain "changed structurally forever", according to Welsh.
And while Welsh is happy to point the finger at Thatcherism for much of the damage done to society he is also critical of successive governments for not addressing the problems of "under-employment" and "people on housing estates being cut off and ghettoised".
He said: "That social fabric was never repaired under New Labour.
"It was a more benign continuation of the same policies.
"Now we are in the same position with the current Coalition government, who are getting back into that paradigm of more tax cuts for the rich and hammering everyone else."
Welsh said that when he wrote Trainspotting he was more interested in taking the reader into the character's world than telling them how they got there.
He added: "But now being a bit older and a bit more reflective on things, I probably have a bit more confidence in myself as a writer to look at some of the bigger themes about cause and effect."
He said his characters all ended up together doing the same things, but for different reasons.
"For Spud, for example, there is a collapse in manual work and he's never going to work again almost.
"At that young age he feels redundant and worthless. So the excitement he has is being part of the drug gang.
"With Renton, it is much more complex. I think he feels he will actually benefit from Thatcherism, from that individualistic culture.
"But while he will personally be ok, I think he realises that his family, his friends, his community are going to be crushed by it.
"With him it is almost perverse way of showing solidarity with them."