I was adopted into a respectable family — Mum was a secretary, Dad was an accountant — and I grew up surrounded by toys, with a doting father who dropped everything the minute he came home from work to play with me. The abuse started when I was 12, cranking up when I was 14 and my mother left. My father convinced me that what we had was really special. He was the only person I had, so however hideous things were, it seemed 100% better to stay with him than have nobody. It may have been a distorted love, but it was the only love I knew. My dad was everything good and everything bad, all in one person.

Weekends were the worst. On Friday nights I felt the world closing in on me because it was just him and me, and I knew what I was in for. A special day was simply a day when I didn’t have sex with him. Food was another form of control. He was either stuffing me — he’d take me to McDonald’s after I’d had my tea — or I’d get nothing at all to eat for days.

As time went on, Dad found new ways to hurt me. When he raped me, he used knives and bottles. Then he brought his friends — one of them was my friend’s father. That was the most difficult thing. I was always thinking: “Is he doing this to her as well? Or am I saving her?”

I never asked, so I never knew.

I can clearly remember the first time I cut myself. It was a spontaneous act with a tin opener. I was so distressed, I felt as though my head would explode.

I drew the tin opener across my arm and felt a rush of relief as the blood flowed. There was an element of “This is what I deserve,” and a feeling of satisfaction that I’d scarred myself. I cut in places people wouldn’t see. My stomach was a favourite, then my thighs and my upper arms. Nobody ever noticed.

After Dad brought his friends in to have sex with me, I’d attack myself in the bath, cutting deep, parallel tracks across my arms with a blade. In a world where I had no control over anything, I was in control. Other times, I’d plan it down to the last detail. If I was having a really bad day, I’d say: “Tonight at 7pm I’m going to cut myself 200 times.” Dad recognised it as a coping strategy; he’d even join in. He used to stub cigarettes out on my arms, and my self-esteem was so low, I felt I deserved it. At times the gashes were so bad I’d have to go to hospital and then he’d get really angry — because I’d put him at risk.

A social worker was the only person who suspected I was being abused, and she persuaded me to tell the police. The officer who questioned me began: “Your dad’s a very respectable man...” It was a case of me having to prove what he’d done. The investigation collapsed before it even started. That gave Dad supreme confidence. It made him untouchable. After that, everything got worse. There’s an appalling letter in my file from the police to social services that says: “Due to more urgent cases, we’ve not had time to look into this matter.”

Self-harming kept me alive. I’d let out all the pain in my head, which stopped me slashing my wrists or taking tablets. When I was utterly desperate I’d ring the Samaritans. I had a befriender called Fran who understood. Instead of trying to make me stop, she’d listen and say: “Have you got antiseptic? Bandages?”

I last saw my father on my 20th birthday, but he still phones. I don’t hang up — I try to manage the call. But when I put the phone down it’s as if I’m 14 again and it takes me days to haul myself back. I’m not angry, but there’s a lot of sadness because I can’t get the answers I want. For so many years I was waiting for him to explain why he did what he did. But what would an adequate answer be?

I’ve been in relationships with others who self-harm. There are no boundaries; it gives you permission to carry on. I’d carry a kit with me — blades, bandages and antiseptic. Then I became involved with someone who said: “If you carry on harming yourself, I can’t stay in this relationship.” That was quite helpful. I’d done all the counselling, I knew why I was self-harming, but I needed to stop for me, and that’s taken years. I talk now, instead of bottling everything up. I tell myself: “It’s okay to feel bad. Just find a good friend to talk to instead of cutting your body.” If it’s a bad day I still look on my scars as something I deserved.

At the Samaritans I occasionally get a call from a girl who sounds like me, and while I can’t change what’s happening to her, I can help. When I was self-harming I didn’t want anyone to try to solve the problem; I just wanted them to say: “Tell me how you feel and I’ll be with you while you’re feeling like this.” I don’t do it any more, but if anything bad happens to me — contact with my dad is always a catalyst — it’s still my first thought. Just giving myself the option is enough. But it’s an option I choose not to take s

Sophie Andrews’s book, Scarred, is out on March 20 (Hodder & Stoughton, £12.99). She uses a pseudonym

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