AROUND three-quarters of the way through writing a book, Iain Banks's mind is already racing ahead to his next project, sketching out plot lines and shaping characters that will inhabit his weird and wonderful fictional universe.

The glimpse into the creative workings of one of the UK's most popular novelists may help to explain why he is also one of the country's most prolific, with 23 novels - both traditional and science-fiction - now under his belt.

It was one of hundreds of unique insights offered to audiences at the Aye Write! literary festival held in Glasgow over the past nine days.

Organisers hailed the event, for which The Herald is media sponsor, as a raging success. It began two years ago as a bi-annual festival at the city's Mitchell Library and wound up last night as a bold new annual fixture on the UK literary circuit.

As the curtains closed on festivities yesterday, an estimated 25,000 people are thought to have attended, including thousands of school children and visitors to the community programme. They heard from novelists, historians, illustrators, politicians, artists, activists and comedians, including some of Britain's best-loved writers.

Karen Cunningham, head of libraries at Glasgow City Council and the event's organiser, said it had been a huge success. "In our first year we had 15,000 visitors and our aim was to match that so to get so many more has been fantastic. I'm really excited about the way Glasgow has responded to the programme. I hope there has been something to appeal to everyone," she said.

Interest had been expressed by major publishing houses and authors in taking part in future events, ensuring that the festival could happily transform from being a bi-annual event when it was launched two years ago to an annual fixture, she said.

Charles McGhee, editor of The Herald, also praised the festival. He said: "The Herald is delighted to have been media partner for the Aye Write! festival which has firmly cemented our relationship with the Mitchell Library, two great Glasgow institutions which value and treasure the power of the printed word.

"All credit must go to Karen Cunningham and her team at the Mitchell who have put together such a wonderful programme that it is already attracting substantial interest from some of the country's top authors who want to take part next year."

Karen Tighe, acting head of sponsorship at Bank of Scotland, which sponsored Aye Write!, said she had been "delighted" with the festival and the bank's involvement.

Iain Banks, who was in conversation with Rosemary Goring, The Herald's literary editor, at the festival's closing event, spoke about the creative impulse which has guided him since The Wasp Factory was published in 1984.

Responding to a member of the audience who wanted to know why he did not take longer over his books, Banks said: "I get bored. I always want to get on to the next one. As I'm re-drafting my books, my thinking process about the next book always takes over.

"At the moment I'm half way through writing a science fiction book and have forgotten most of this one."

Banks also delivered a robust defence of the science fiction genre which, he said, was "one of the most important genres in literature, certainly since the industrial revolution". It was, he added, essential reading for "anyone who finds technology and the pace of change exciting."

Banks has sold his sports cars - two Porsches, a Jaguar and a BMW - and bought a fuel-efficient hybrid Lexus RX 400h worth £40,000, after becoming ashamed of his carbon footprint.