Libby Purves explains to NICK UTECHIN why she is speaking at the Oxford Literary Festival about her son's death

The broadcaster, novelist and columnist Libby Purves comes to the festival with a real challenge: to speak of her own son's death. Nicholas took his life, at the age of 23, in June 2006, after some years suffering from a mental illness that his mother, inevitably, finds complicated to discuss.

"There was this fragility. It seemed to develop into frightening, perhaps psychotic symptoms -way beyond normal depressions. And I suppose that is what got him. He was very reserved, very dignified, very uncomplaining, still witty and sweet with us, good company until his very last day. And we knew from his notebook that he resisted suicide, several times, bravely."

After his death, Libby and her husband, Paul Heiney, searched for any background available to the life that had gone. There were random writings, scribbles on Post-it notes, detailed records of sailing expeditions. None of it was formally laid out for the public to read. But Nicholas did write once: "My goal is to write something I could show to somebody" and thus gave permission of a sort. And so the book of his posthumous writings, The Silence At The Song's End, edited by Libby and Duncan Wu - Nicholas's Oxford tutor at St Catherine's College - has appeared, selling some 4,000 copies thus far. Duncan Wu will be joining Libby Purves in a joint session.

"It was Duncan," Libby told me, "that saw we had 'no alternative' but to publish. And he is no sentimentalist: he's an English literature professor with a reputation to preserve. Nicholas lived by books - he loved his Oxford course, read immensely widely for his last seven years, respected and loved the community of novelists and poets to whom he responded so passionately. He deserves, and would want, to be a member . . . a junior, small-time member . . . of that community."

The book's title comes from a poem written by Nicholas a year before his death . . . . I sing, as I was told, inside myself.

I sing inside myself The one wild song, song that whirls My words around Until a world unfolds.

My ship's new sail I catch the dew and set A course among the ocean curls The silence at the song's end Before the next Is the world.

There are desperate lines in his writings: "There is something rotten within me. I know this because I see it everywhere. My rottenness is the world around me." How hellish was that to read for his mother?

"This is a symptom of profound, dangerous, potentially psychotic depression. He did not feel that way all the time: this we know. But we also know enough about the illnesses of the mind to recognise what it was." And then, more buoyantly: "Remember, this outbreak of depression and despair was very early - he was only 18. And as it goes on and as he makes his sea voyages, he gains a much wider human perspective, often grandly so: saying extraordinary things like: 'Remember how the streets ring out for every soul that thought and felt and walked through them, in weakness and in strength.'"

There is a characteristic sturdiness and professionalism in Libby's preparation for the festival.

"I will introduce the book and Duncan and I will discuss it together. It's the first time I have done such a thing, but it's Oxford, and that is a priority. I suppose, too, that I am doing it for Nicholas's honour - in the old-fashioned sense of the word. As for what I might feel myself, standing up there - hell, it's a fleabite compared to the personal loss."

In a subtle piece of casting, the festival organisers have also invited Libby to be an interviewer in another session: talking to Christina Hardyment about the latest edition of her book on child care, Dream Babies. They are personal friends: "I admire the way she brings not only humour but academic rigour to the study of domesticity down the ages. When Nicholas was new, 25 years ago, and I was a confused new mother being bossed about by fierce baby-gurus, I picked up Christina's book and realised that basically all baby-gurus have tended to be a bit batty, very opinionated and ludicrously influenced by their own culture. So they should be taken with a large pinch of salt."

Libby is hardly a stranger to Oxford and spends much time in the city. Her latest novel, Love Songs and Lies, portrays 1970s' student life in the city and, "and the crummy house we rented with water under the floorboards, and being in love with inappropriate blokes . . . who needs a shrink when you can put it in a novel?!."

She honed her broadcasting skills at BBC Radio Oxford, before famously moving on to the Today programme. She has a good memory of those early reporting days: "I still go misty eyed at some place names and wish I was up in Summertown reading out the What's Ons, or sitting next to Richard Early at his old loom in the Witney blanket factory, or with the Headington Morris men on May Morning, or doing a live New Year party in Wolvercote Village Hall. I almost belong."

The Silence At The Song's End, edited by Libby Purves and Duncan Wu, Songsend Books, £12.95. Libby will talk about the poems at the festival on April 4 and will also interview Christina Hardyment about the history of childcare on April 5.