To Saughton prison, a particularly apt place for Irvine Welsh to talk about his latest novel, Crime. Saughton's prisoners were the first to hear him reveal that he's writing a prequel to Trainspotting. "As you get older you get more reflective, more interested in cause and effect," Welsh said.
"Now I'm more interested in the personal dynamics between the Trainspotting characters, and between them and their families. It's quite interesting for me now to revisit all of this, whereas it wouldn't have been a while back."
The book will be called Skagboys, and it will be set two or three years before Trainspotting. It will chart their lives and loves "from a casual interest in speed, sex and football to full-blown smack addiction".
The prisoners, all big Trainspotting fans, were less than convinced by Welsh's latest novel, which is set in both Florida and Edinburgh. "It's like, you're watching Doctor Who and it suddenly turns into What the Romans Did for us," said one.
The sequel to Trainspotting might be going places too, Welsh also revealed. On Monday he had talks with Andrew Macdonald and Danny Boyle, producer and director respectively of the iconic 1996 film, about the possibility of filming its sequel, Porno.
"We're just going back to basics and seeing what will happen. There's never even been a script, and I don't even know if they'll want me to do one," said Welsh.
Industry insiders have hinted that the main problem was Ewan MacGregor's reported reluctance to reprise the role of Renton. "I met him at an awards bash in January and he was saying there was hardly any mention of Renton in Porno," said Welsh, "so perhaps we'll have to have another look."
Candidly, Welsh admitted that the main fault might be that the two plots in Porno – the shooting of a pornographic video and the backstory of the Trainspotting characters – didn't hang together as neatly as they ought to have done.
Saughton's library has about 4,000 books, although not as many of the 800 prisoners use it as the authorities would like. There's one way to change that – but it would cause problems.
"If we wanted to," said its librarian, "we could fill the shelves with true-crime books by people like Reg McKay. They'd fly off the shelves. Trouble is, they wouldn't fly back."
Prisoners, apparently, tend to hang onto books about gangsters, and go in for macho boasting about how they know the hard men they are written about. The result is that the books stay on the cells' shelves, and are seldom returned. In prison, it seems, no-one worries about library fines.