Her last book – the bestselling Orange Prize-winning We Need To Talk About Kevin – focused on the difficult relationship between Eva Khatchadourian and her son Kevin who, shortly before his 16th birthday, commits a Columbine-style massacre at his high school, killing nine people.

The much-talked-about book that made her famous is told in the form of letters written by Eva to her estranged husband Franklin after the killings. Eva is the archetypal unreliable narrator, in the sense that every incident which seems to support the idea that Kevin is a cold, calculating sociopath is described from her point of view.

Yet Shriver cleverly ensures that there is a possible entirely different, less damning, explanation for each incident – and Kevin's part in it. In this way, the book has, since its publication in 2005, dramatically fuelled the nature-versus-nurture debate, as well as discussion about the notion of absolute evil.

Shriver, who spoke at the Ilkley Literature Festival yesterday, said she could not have known how controversial the book would become.

"I tend to write in a sort of state of naiveté and, anyway, you can't keep second-guessing your audience. However, I was writing from the perspective of a character who I knew was going to be unsympathetic from the start – it's quite unsympathetic for a woman not to like her child – so I wasn't so naive as to think that it wouldn't provoke some reaction."

Eva does, however, have many redeeming features – not least of which is the fact that she constantly questions whether her ambivalence towards, and inability to bond with, Kevin may in some way be responsible for his horrific actions as a teenager.

"I think the character does redeem herself through her honesty," says Shriver. "That is her primary redemption – at least she is upfront about her feelings."

Nevertheless many readers found the book supremely discomforting and were outraged by its portrayal of such an "unnatural" mother. Others, however, were impressed that Shriver had had the courage to confront such a difficult issue.

"I have been mostly exposed to women who found it liberating," says Shriver. "I think we have sentimentalised motherhood, and I feel that parenthood is often portrayed in art in a candy-coated way. I'm not saying that parenthood is an unrelenting hell on earth, but it does test you. There are parents who experience moments of dislike and antagonism towards their children and I think for many it has been a relief to see that addressed somehow."

What is quite striking about the novel is the way in which Shriver, who is not a mother, gets so completely under the skin of Eva and makes her into such a believable parent. "It wasn't a case of doing a lot of research or interviews. I guess I paid attention when my friends talked about their children.

"Otherwise it's just the product of an over-active imagination and over-active fears – what would
it be like if your child grew up to
be a killer? Also, when I was writing the book, I was in my mid-40s and on the cusp of making a decision about whether to have children or not and I think that fed into my writing."

Shriver's theory about her decision not to have children – which she says she feels "at peace with" – is interesting. "I think the reason I didn't have children is partly because I didn't get my career off the ground until my mid-40s and that created in me a kind of extended adolescence. I don't want to compare books to children but my primary preoccupation was my novels."

The Post-Birthday World is another searingly honest exploration of human relationships. With the same fearlessness that characterised her study of motherhood in We Need to Talk About Kevin, she examines relationships between men and women in their forties and the lure of the exotic over the domestic.

It focuses on the struggle of Irina, an American illustrator living in London, torn between two very different men – her steady long-term partner Lawrence, who is also American, and attractive, successful English snooker player Ramsey.

"I was once in the position of trying to make up my mind about two very different men and I took that quandary and spun it forward," says Shriver. The form the novel takes is to follow the two different directions that Irina's life could take.

"When, in real life, you are dealing with these kinds of issues and trying to make a difficult decision, you have to spin out your future in your mind," says Shriver. "I wanted to explore how much difference it makes whom you choose to love."

One element that makes her writing so engaging is the strand of dry humour that is present even when the subject matter is dark or troubling. "I think that humour is a tremendous coping mechanism," she says. "I think traumatic experiences become manageable if you can inject some humour.

"Imagine if you are on a trip abroad, for example, and everything goes wrong – what do you do? You crack jokes in order to redeem the experience and then, later, it allows you to remember those experiences with affection. It's a whole way of life for me – not taking it too seriously."

The Post-Birthday World is published by Harper, £7.99, and We Need To Talk About Kevin is published by Serpent's Tail, £7.99. To order from the Yorkshire Post Bookshop, call free on 0800 0153232 or go online at www.yorkshirepost
bookshop.co.uk. Postage and packing is £2.75.