I became aware of how cruel children can be to one another in fiction before I encountered it again in life, but in the late 1960s I went to write a book in a remote Dorset cottage. Two boys aged 11-the farmer's grandson and a friend, came by most days and if they took the left-hand track were hidden from my cottage garden by a high hedge. It was a beautiful summer and I was often working at a table in the garden. I heard what they were saying to one another. Sometimes, it was innocent back-chat between them but then I detected an unpleasant tone in the voice of one boy. It took me little time to realise that he was a nasty, spiteful, unkind, mean, cruel child bullying his "friend" with threats and frightening stories. To my horror, I then learned that they were going to boarding school together the following autumn. What could I do or say? I remembered Michael so clearly and wanted to save this poor boy-who was small, thinner, fairer and very vulnerable-looking-from his thug of a companion. I waited until they went by the cottage one day and when I overheard something nasty, shouted out loudly. The boys fell silent. They did not take that track again and when I met the bully in the lane, he stared me out. 

I asked the adults if the boys got on all right together-how could I phrase it more strongly? They laughed and said they were "the best of chums". The sound of their hearty, confident voices, the obtuseness of their reply, was so chilling that I could not get it out of my mind and the next day I made a few notes about parents and other adults who know absolutely nothing about their children and their lives, who cannot see what is happening and will never be told. I knew that if the bullied child had ever said a word his father would simply have laughed at him. 

The boys left and my notes became a novel, I'm the King of the Castle, which I wrote very quickly during what was left of that summer. It is based on the two young boys I had seen and heard on the farm, the cruelty of one, the misery of the other, and the obtuseness and selfishness of their parents. Forty years later, it is a set book for GCSE and is taught in many schools. It was not written for young people but they are the ones who respond to it best because although teenagers in 21st-century comprehensives are very different from prep school boys in the Sixties, the behaviour, the subject matter-the inner misery and fear, the cruelty and the need to stay silent, let alone the incomprehension of adults, are completely familiar to the young now, as then. I have occasionally visited school classes in which 14-year-olds are discussing the book-neither I nor the teacher needs to say anything, the pupils speak, argue and debate the issues among themselves. It is very gratifying to hear them and to know the novel strikes such a chord. 

But some parents, over the lifetime of the book, have objected both to the theme, and more, to the ending in which the bullied boy commits suicide. I have had letters telling me categorically that "of course this never happens". But it does. It has gone on happening from time to time over the 40-odd years since I wrote the novel. It happened again recently, when a young girl killed herself because she could take no more cruelty and unkindness-or "cyber bullying", an especially nasty form of it, which was unheard of when I wrote my book.