He wrote: ``Alzheimer's sufferers are not always gentle: I know that. But Iris remains her old self in many ways. The power of concentration has gone, along with the ability to form coherent sentences, and to remember where she is, or has been. She does not know that she has written 27 remarkable novels, as well as her books on philosophy; received honorary doctorates from the major universities: became a Dame of the British Empire.

``If an admirer or friend asks her to sign a copy of one of her novels, she looks at it with pleasureand surprise before laboriously writing her name and, if she can, theirs. It takes her some time, but the letters are still formed with care, and resemble, in a surreal way, her old handwriting. She is always anxious to oblige. And the old gentleness remains.''

For some years, the illness had ended but not dimmed admiration for the prolific output of a woman who was widely seen as perhaps the most luminous, intelligent and inventive novelist to emerge during the post-war years. Her last book, the study in religion and philosophy, Existentialists and Mystics, was not published until 1997.

When her first novels, Under the Net, Flight from The Enchanter and The Sandcastle, burst into print from her untypical background as an Oxford philosophy lecturer in the mid-1950s, she was seen as a writer who might become a major modern classic, a new George Eliot with touches of the passionate imagination of a Bronte.

This wild hope receded as the years past. But she was always in the front rank of unpredictable,original, serious writers exploring the deeper themes of ancient as well as contemporary experience. Her fellow-novelist Malcolm Bradbury, paid tribute. ``If one was to compile a list of the best five English writers since the war, she would be up there.''

A.N. Wilson, who is writing a book about her, said he was very distressed at the news: ``The novels were successful because they spoke to a generation of people who are making up their lives as they go along and finding that it doesn't work; they describe lives of emotional and intellectual chaos. She was the most serene, generous person who was kind and good. I think her emotional strength came from her extraordinary marriage to John Bayley. I last saw her six or seven weeks ago, she was in a dreadful trance-like state, but she kept the sweetness of her nature. She kept smiling.''Critic John Casey said: ``She was the nearest we have in England to Sartre.'' The critic Frank Kermode called her a ``very serious and brilliant person but not in a heavyway''.

He added: ``She was extraordinary both as a novelist and a philosopher. I think her work will endure. She inspired a certain kind of awe; although it was fun to be with her, there was no sense in which triviality was permitted. She had a kind of earnestness that was very charming but you felt how very much more intellectual she was than you. She wasn't just a nice person, you felt she was a good person too''.