In some ways Nightshade Mother, your new prose book, is heartbreaking. Somewhere you say that writing it is killing you, and the reader knows exactly what you mean. But elsewhere you explain how language gives you the resources to do the job. How did the whole thing come about?

I’ve been planning this book since I was in my early twenties but, despite having written about a tough subject, depression, before, nothing could have prepared me for the difficulties of this task. Part of the emotional abuse I suffered at my mother’s hands involved her hijacking my writing at an early age, so the subject was like turning the knife I’d been wounded with back on myself again.

I’ve always trusted form to shield me from explosive subjects, so I was surprised to find that, in writing the first draft of this book, I’d retraumatized myself and felt suicidal. I hadn’t allowed myself to look at the full extent of the abuse before and it was worse than I’d realised. So, initially, the writing was the opposite of therapeutic and required a lot of raging and grieving. However, with the final version, I’m finding relief in getting the story out of my body and into the world.

I spent years writing of elaborate techniques that implied what happened without spelling it out. I worked out overall schemes, involving tarot cards and various metaphors, such as James Tilly Matthews’s ‘Air Loom’, until eventually I found that I could use text – letters, diaries – as a way through ...