Terry Pratchett, who was a journalist in Bath and Bristol before becoming a full time novelist, had a huge welcome at the Forum when he celebrated 25 years of his Discworld novels by speaking on the opening day of Bath Literature Festival.

The quirky humour which pervades his novels was apparent in his conversation with festival direction Sarah le Fanu.

He talked about and read an excerpt from Nation, his next novel, due out in September and at the end of the evening he auctioned the sheets of paper from which he read, raising £425 for the Alheimer's Society.

Pratchett announced recently that he has been diagnosed with early onset Alzheimers and said he went public to get people talking about the disease and doing something about it.

He said: "I started off feeling so alone and then I began to rattle cages. You can't be ashamed of an illness. People used to not talk about cancer, but once they did, people began to work towards finding a cure."

He spoke of his childhood obsession with books which found him working in Beconsfield public library for nothing on Saturdays so that he could have access to 156 library tickets.

He also revealed why he wears an Edwardian smoking cap when reading in his library at home. It is to prevent him damaging his head on the stone lintel over the fireplace when he stokes the fire.