IT'S ALMOST LIKE EUTHANASIA WOULD HAVE ROBBED HIM OF SOMETHING VALUABLE:

So persistent and alarming have been the advance warnings of Sir Terry Pratchett's impending mental decline that the oddest thing about meeting him is his apparent normality. It is five years since the comic fantasy fiction author announced his "embuggeration" , a very Pratchetty way of describing a diagnosis of Alzheimer's disease. By now, you fear, he will be slowing up, imagination fogged, creative powers shrivelled as a walnut.

Instead of that, the little man in black is a delightful affront to medical science, looking wizardly well in his black fedora with a jaunty feather in the trim. His handshake is firm, his eyes piercingly bright. He talks for 90 minutes with great fluency - although it does occur to me after a while that his habit of answering questions with an anecdote, or another question, may be a way of playing for time.

A new book is out, one of three he is working on this year. Since the diagnosis, he has made two television documentaries, continued his international book promotion tours and become an industrious ambassador for assisted dying. Is this one miraculous burst of defiance before the dying of the light, or did they somehow get it wrong?

"I have to tell you that I thought I'd be a lot worse than this by now," he says. "And so did my specialist. At the moment, it's the fact that I'm well into my sixties [he is 64] that's the problem. All the minor things that flesh is heir to. This knee is giving me a bit of gyp. That sort of thing. And I'm well into the time of life when a man knows he has a prostate. By the time you've reached your sixties you do know that one day you will die and knowing that is at least the beginning of wisdom."

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