It is a very peculiar sort of controversy. In an episode that turns the standard sex scandal on its head, the author John Bayley, husband of the late novelist Iris Murdoch, stands accused of not having sex with two women whose not entirely unwelcome advances he describes in the latest volume of his memoirs.

In Widower's House, an account of his life since the death of his wife in 1999 to be published on Wednesday, Bayley, 75, describes being hounded by two women, Margot and Mella, both of whom successfully press themselves upon him. Last week the Daily Telegraph ran extracts from the book, illustrating them with photographs of actresses knocking at the author's front door and mopping his kitchen floor. A footnote to the extracts reads: "Some names and minor details have been changed to protect the identities of those concerned."

The first two volumes of the memoir, which chronicle Murdoch's six-year struggle against Alzheimer's disease, reaped commercial success and critical acclaim. The first volume, Iris, was a surprise bestseller in 1998, while the sequel Iris and Friends, a distressing chronicle of her last days, was described by one critic as "the greatest love story of our age".

Yesterday, however, Bayley acknowledged that in Widower's House he had strayed into the realms of fiction, conceding that the amorous pair, a 30-something undergraduate (Mella), and a family friend (Margot) do not exist. Rather they are "composites" of real people.

Speaking from the Oxford home he shared with Murdoch and now with his second wife Audi, Bayley defended his decision to employ the techniques of the novelist when writing Widower's House.

Vulnerable

"It's simply that they are composite characters, they are both real and unreal. I obviously can't make a faithful portrait of people I know so I combined these various persons in the same way a novelist would," he said. "Characters are made up of people and things you observe. The two characters have their own sort of reality. They just sort of come to you. Most novelists will tell you it just happens, that they find themselves with a character who obviously has features of real people.

"I don't think of this being a novel. It is intended as a comedy on the theme of bereavement and what happens when one is all at sea, when the certainty of one's existence comes to an end.

"The point is to show what it is like to be in this very vulnerable situation. One is not allowed to get over it in one's own time... people always want to help," he said. "If you have been looking after someone for five or six years it is like being in a monastery, and when you are let out into the big wide world you hardly know what's happening. It is that situation I am trying to describe."

In the book Bayley writes of the unwanted attention he received after Murdoch's death, and the loss of the protective cloak of marriage. "Out of the ground had sprung a host of well-intentioned persons who wanted to make life nicer and less lonely for me... Widowers are prey to the whims of kindly women," he writes.

Chief among the predatory ladies, according to Widower's House, is Margot, whose first act is to cook him a casserole - "I have always disliked casseroles. During our 44 years Iris and I never made a casserole" - and later joins him under the duvet in the spare bedroom after inviting him to her Norfolk home for the weekend. "I remained as immobile as a spider trapped in an empty bath and uncertain in which direction to run. Margot's ample presence, now she had settled down, was indeed comfortable rather than the reverse, but not exactly comforting," he writes.

Mella, an undergraduate who "marks her territory" by cleaning the house, is more direct. "Slight and straight" in contrast to the "dark, ample, dynamic" Margot, Mella lures the innocent academic into her arms by feigning a dizzy spell and going to lie down upstairs. When he looks in to see how she is, she pounces.

"She sprang up, threw her arms around my neck and gave me several kisses at random. She continued to hug me, and I I did my best to detach myself. She pulled me down beside her on the bed. At least we were both fully clothed... A couple of hours later we were not."

Reflecting, Bayley writes: "It was ridiculous to have been manhandled as I had been by a slip of a girl. But there I was, an old gentleman who had never been particularly strong at the best of times."

While acknowledging that Mella and Margot were in essence fictional, Bayley yesterday remained coy about the practicalities and key events of the relationships on which they are based.

"It is true to say that I did have some sort of relations of that kind. The practicalities are made up but the relationships existed. The relations described and the people do exist, but they are changed." He added that he had not remained chaste after Murdoch's death. "Lots of people have sexual relations do they not?" he said.

Corinna Honan, assistant editor (features) of the Daily Telegraph, said: "We went ahead with the serialisation of John Bayley's new book after receiving categorical assurances that all major events in it actually took place. It was always understood - as both Jan Moir's interview with Prof Bayley and our extracts last week made plain - that certain details including names had been altered in order to protect the identities of 'Mella' and 'Margot'. "

John Bayley: a life in letters

• Born 1925

• After Eton, serves in the army from 1943-47 before gaining a first in English from New College, Oxford

• Member of St Antony's and Magdalen colleges 1951-55; tutor at New College 1955-74

• In 1956 meets and marries the love of his life, Iris Murdoch, at that time herself an academic with a fledgling literary career

• Appointed Wharton professor of English in 1974, a post he holds until 1992

• In the 90s Bayley writes widely for newspapers and becomes a highly regarded critic, but in 1994 Murdoch is diagnosed with Alzheimer's disease and Bayley devotes himself to her care

• After her death in 1999 he marries Audi Villiers, a widow and friend of Murdoch. "Audi and I talk incessantly about Iris; never stop, really. It's our favourite subject," he has said

• His greatest success comes with the memoirs Iris (1998) and Iris and Friends (1999), and he has written 15 other books including five novels and academic texts on Tolstoy, Pushkin and Shakespeare