All is revealed in a teenage diary, however embarrassing I have just spent half an hour crawling around on my belly in our tiny, cobwebby, junk-filled attic - for which unpleasant experience, I blame Hanif Kureishi. The novelist has donated his entire literary archive to the British Library: manuscripts, letters and - this is the eye-catching bit - personal diaries, dating back to the teenage years. Most recovering diary-writers, myself included, can find no such consolation. Right at the back of the aforementioned attic, buried under dusty boxes of old records, school reports and childhood oddments, there are 30 or so volumes of my personal diaries. They run from 1984, when I was 13, to 2011, when I turned 40. "Nobody may read this diary - unless with express permission - on pain of death," reads the title page of that very first diary. Sounds promising, no? What follows - "Today we had Music, Geography and R.K. exams. Mummy will be very sad if I fail any exams, but quite frankly it would be nice if I could get 10 out 10 but if not I really feel it doesn't matter..." - isn't just boring; it is also totally dishonest. I was never that girl. The fact that I sound like a goody-goody from Malory Towers tells you something about my reading habits (exclusively Bunty and Enid Blyton), but absolutely nothing about me. Later in my teenage years I adopted a florid, adjectival style - half Emily Brontë, half Just 17 - with which to chronicle the ups and downs of adolescent love. I can hardly bear to read the description of losing my virginity, let alone inflict it on innocent readers. But if I tell you that it contains the words "quash," "lest" and "swirling profundity," you will understand something of my retrospective agony. What bothers me most is not the pretentiousness: it's the realisation that I couldn't tell the truth about myself, even to myself. I was too busy showing off, trying to seem cooler or cleverer than I really was. The fact that I kept up my diary for so long, filling notebook after notebook with half-truths from my almost-life, is a testament to the therapeutic effect of writing - even bad writing. During the long decades of romantic misadventure, I had an empty bed in which to sit and scribble. It was soothing to refashion my loneliness into neat, anecdotal episodes. But after I met my husband and started having babies, the diary-writing petered out - and not just for want of time. This is the happiest period of my life. I would rather have hazy but true memories of it than falsified records. I want to live it - not parcel it up for posterity.