It’s probably very laudable — and certainly very Leavisite — to let a novelist and the book stand apart from each another and be assessed on their respective merits: the author as a person, the book as a piece of fiction. But there are instances where such scrupulous acts of separation are not only hard, they also border on the perverse, so convinced are you that you have been reading something close to autobiography. I am looking at one such now, in the form of Graham Swift, having previously been looking at his most recent book, Tomorrow.

For Swift, location is as significant as it is for estate agents, and here we are, right in his South London patch, also the setting for the book. There is a sense in which the place has been degraded in the act of improvement, a recurrent thought in the novel, with its sweep that virtually parallels the author’s, both starting just after the war.

The traffic-calmed roads seem to increase congestion, the pedestrianised bits are slightly twee, and the big pub has fallen to gastro-itis.

Tomorrow is the story of a middle-aged couple, Mike and Paula, whose professional lives encompass publishing and the visual arts, as the lives of the Swifts have broadly done. The couple in the book face a crisis, and it will come to a head on the following day, the 16th birthday of their twins. Or to be more precise, her twins, Mike’s low sperm count having disqualified him from procreation. The dilemma of what to tell the children possesses Paula to such an extent that her whole testimony is like one mighty tug between her and her husband’s genetic histories on the one hand, and the legacy of gaps and mystery left by the anonymous donor on the other. And what about the grandmother? Has she somehow known all along that the grandchildren are not, strictly speaking, hers?

It was, above all, the sympathy with which Swift casts a parental projection into the twins’ possible range of responses that made me suspect some direct experience of such nightmares. This made me ponder intrusive questions about his own fertility. I should have known better, having read his two most celebrated books, the Booker-winning Last Orders and the shortlisted Waterland, and several more besides.

The whole trick of his writing is to produce complete emotional veracity, or at least the illusion of it, in the lives of quite ordinary English people. It was evident with his debut novel, The Sweet Shop Owner, published 27 years ago, in which the character of the title waits for his daughter’s return as he approaches death; then Shuttlecock a year later, about the collapse of a family beneath a weight of history comparable to that borne by the heroine of Tomorrow.

“We have no children,” Swift says, as if anticipating a question. “Out of choice, so the subject of this book is fiction, and in no way autobiographical. We have no regrets about it. Obviously, now, it’s a rather academic consideration but, when we were younger, when it might have been a pressing consideration, we just came to an agreement that we didn’t really want any children, and this has just carried on. In some ways I feel the opposite of regret, from what I have witnessed with the families of friends.”

What’s happened, he agrees, is that the story has turned into a harrowing account of unearned desperation. When the twins were conceived, the donor’s anonymity was protected. One-and-a-half turbulent decades later the rights of the young adult to know his or her genetic origin had become paramount. So couples acting in good faith to produce and nurture life found themselves criminalised by a (correct) shifting of values.

“I kept wondering what would I have thought if I were 16 and in that situation. Would my feeling be that I had been lied to, or would I accept that this was simply how it had had to be? I do know that these things are massively important, and affect people’s whole lives dramatically.”

Not that he set out to write a documentary or sociological novel. The notion of intention, or the lack of it, throws up another child-related question. Aren’t these his books like children? He seems to clear his life for their making, thinks of little else while producing them, then watches with pride and anxiety while the world decides what to make of them. “One of the things I most enjoy,” he says, “is when people come up to me, as they have quite often done at Edinburgh, and just said things like: ‘I was in North Africa, and I knew people just like that’, after I’d been reading from Last Orders.”

We return briefly to children. They can be a dangerous analogy, he says, particularly with books like his new one.

“There is some viability to the theory, but I would not go too far down that road. I do like to have books that acquire a sort of personality, and they have a separate life with readers, which is pretty good. But when you are making them, and after you have made them, they are beyond your control.”

Well, quite.

Graham Swift, Monday, August 13, 11.30am, RBS Main Theatre, will discuss Tomorrow in one of the festival's Meet The Author events

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy