As people who hate doing interviews go, Sebastian Faulks must be the most obliging of them all. After all, he ends up doing this interview twice. Once over several pots of tea in Dublin. Then later in the week, after the original conversation has been wiped from the recorder, writes Shane Hegarty

"We are all at the mercy of technology," he says, before putting himself once again at the mercy of a journalist's ineptitude

The novelist has good reason to be wary of journalists: he used to be one. He knows that once his words are given to a reporter there's a chance they'll get bent out of shape, paragraphs will be rearranged, the story diluted to one easy hook. Besides, it is the current fashion that the interviewer will try and psychoanalyse the subject over the course of the hour. Particularly, it seems, they like to psychoanalyse Sebastian Faulks.

Interviewers often seem to be deeply concerned with the exact timbre of his accent, quite how public school he might be, even the precise wooliness of his hair. He much prefers question-and-answer interviews. Ones in which they ask you what your favourite food is, or your favourite colour. They're far more interesting, he believes. And what is his favourite colour? "Purple."

In his latest novel, Human Traces, psychoanalysis features large. It is the story of Frenchman Jacques Rebiere and Englishman Thomas Midwinter, each with the ambition to understand madness at the turn of the century, when a rift would open up between those who believed mental illness was genetic, and those who wondered if it was caused by experience. Jacques is keen to find a cure for his brother whose illness is unnamed, although the reader recognises it as schizophrenia. Like his most famous novel, Birdsong, which recreated the trenches of first World War France with awesome detail, it fulfils Faulks's central ambition to write about the impact of public events on personal lives, and what happens when two worlds collide. Yet, as Faulks is adept at, it retains intimacy and humanity.

Faulks has always been interested in why people's minds sicken, and whether their illnesses can tell us something about ourselves in health. As a child, it was mere curiosity, but "as we get older, we lose that amazement because we grow used to people being insane. But in fact it really is bizarre. You do not have paranoid donkeys. Pigs do not hear the voices of four or five non-existent pigs talking to them loudly all the time. Psychosis is a human condition. The question is whether it is the human condition - in other words what it tells us about the nature of homo sapiens. If, as a novelist, your interest is in human nature, then it makes sense to look at it under extreme pressure - as it were, to find its boiling or melting point. In Birdsong, this was with men facing annihilation; in Human Traces it is with minds that have broken."

Schizophrenia, he says, is an illness that "seems to caricature ordinary life, to make a mockery of ordinary happiness". He once lived next door to a young schizophrenic, whose mother simply told Faulks that "he lives in hell".

"But like all my novels Human Traces is a work of imagination. It is not 'based on' or 'inspired by' actual people or real events. I was appalled by a headline in a London paper that suggested I had been 'inspired' by events in my own family. My mother had a minor emotional blip in her 30s that she quickly overcame with characteristic resolution; she enjoyed good health all her life. I had a couple of minor blips, too, in my 20s that seem in retrospect banal. They have nothing whatever to do with the serious illnesses that are the theme of Human Traces."

The novel contains tremendous historical detail; a little too much, according to some critics, who worry that his intensive portrayal of the period's academic fervour pushes the characters to the margins. Faulks has said how it frustrates him that people tend to ask about the research rather than the words. With Birdsong, it is the detail of the trenches that people remember, and he is commended for being an exhaustive researcher. Yet, good research alone does not explain why it has sold two million copies.

"I would say that my novels are really 70 per cent words and choice of words; 25 per cent imaginative empathy; and five per cent research. But that five per cent is rigorously checked. By about 20 people in this case," he explains.

"If readers are surprised by these proportions, then that is fine by me. It's good to have some mystery about your art. I remember a very clever but not literary man asking me to explain once how I got the intensity of feeling into Charlotte Gray. He kept on probing. I couldn't understand what he was getting at until eventually it occurred to me that he had not even considered that the choice of words might have anything to do with it. He was gob-smacked when I explained.

"I am happy that the bulk of what I do - word choice - is not recognised or understood by the bulk of readers because when I see them cry or see the book shaking in their hands as they read on the train, I know that the word choice has worked, at a level unnoticed by the reader - which is the best level."

Not since his first novel, A Trick of the Light (1984), has Faulks bothered with contemporary England. Since then, he has toured 1930s France, two World Wars and a Cold War. At 52 years old, he is about a quarter of the way through his first children's book, because he enjoys just making it up for once, without resort to the history shelf in the library.

It'll finally be something his three kids might want to read, given that they have yet to show any interest in his work. Otherwise, though, has he considered moving into the present? "I have written millions of words about contemporary England - in journalism. Why don't I take it as the background for a novel? I may do one day. But the simple answer is that it does not excite the novelistic part of my brain; it does not fire it up. The best novel I have read about contemporary Britain was Money by Martin Amis, more than 20 years ago. But he is a surrealist, basically, and realistic attempts at it are usually very thin."

Writers struggle with England in a way that Americans don't with "troubling, middling America," as John Updike has put it. "Something in the culture seems to rebuff a Roth or an Updike," adds Faulks.

Anyway, he wonders, is it not like asking the Venetian painter Canaletto if he would not like to paint a dry street for once? Or George Stubbs if he'd fancy painting something other than a horse? "Just give a us a fecking cow, George, just once," he jokes. "Next thing you know, that mane had started to creep in . . . "

The new book is also a return - imaginatively at least - to France. It was unavoidable, given that a key figure in neurology of the period, Dr Jean Martin Charcot, needed to figure in Human Traces; but it was a happy excuse. France, he admits, set him free imaginatively. "I had trouble finding a fictional voice in my twenties. It all came out trite and 'comic', but not funny. When I first started visiting France in the early 1970s, the past was much more available than in concreted-over England. It was technologically backward, rural, yet with a sense of secrecy, of shame almost. It just really fired me up in a way that Slough and Maidenhead did not."

With his second novel, The Girl at the Lion d'Or, he "leapt headlong into a foreign country, a different period [1930 and a main character of a different sex. I had discovered the secret of novels, so far as I was concerned: write about what you don't know - invent. So I am forever grateful to the country that set me free. I have subsequently come to know it much better. I grieve for it at the moment. It feels caught between Third World immigration and the hated Anglo-Saxon. If only it had been less dismissive of other cultures over the past 50 years, they could have avoided this crisis. And the food would not have gone off so drastically . . . "

Human Traces is published by Hutchinson, £17.99