and the end of the 10-book sequence, my publishers were telling me that I had sold 19 million copies in 30 different languages. I had become a best-selling author.
Curiously, this has never made as much difference to my life as you might think. I still spend about 10 hours every day on my own in an office, sitting in front of a computer screen - as I am now. Yes, it's a comfortable office. But money has never been a motivating factor for me (my father lost every penny he had and then died, which rather taught me something). I write for a very simple reason. I love telling stories and have done ever since I was a 10-year-old schoolboy.
And yet one thing has changed. Almost despite myself, I have found myself becoming a voice, particularly on issues of child literacy. I am often involved with the National Literacy Trust, a first-class UK charity that works tirelessly in schools and communities.
I have found myself in Whitehall and Westminster, discussing literacy issues with ministers (who have, of course, ignored anything I might have to say). I have talked in schools and universities up and down the country. Just a few months ago, at the Imagine Children's Festival which has become a spring half-term standby at the Southbank Centre in London, I had an audience of about a thousand. Publications as serious as TES occasionally ask me to write articles for them.
None of this was my intention when I wrote my first children's book back in 1977, and I often wonder if I have any right to speak out when others know so much more than me. I'm a writer, not a crusader. My books aren't particularly didactic. They're full of violence and unlikely escapades. What, I ask myself, am I doing?
Well, here's the answer. I've written 40 books, visited perhaps 500 schools and met thousands of children, and everything I have experienced has persuaded me of the astonishing power and the value of narrative fiction.
I often quote a wonderful essay by Jonathan Sacks, The Home We Build Together: "Stories unite. They tell us who `we' - all who live in this place - are. They become essential when a nation no longer shares a common ethnicity or a single overarching religious system of belief."
Reading teaches empathy. It puts back the connections that may be lost when everyone is plugged into their own iPhones and iPads, cocooned from the real world in hoodies or Beats.
If this sounds a touch highfalutin, personal experience has shown me what, to most teachers, will be obvious. Children who read are more articulate, more confident, better informed. They shine. I love the letters they send me, full of intellectual curiosity. When I give a talk to children who have actually chosen to be there, I am always impressed by their extraordinary energy. Adults read books. Children devour them.
It sometimes bothers me, though, that - at Edinburgh, at Hay-on-Wye, at Oxford, at Cheltenham - I am meeting the same children, over and over again. For all the success of Alex Rider, I'm aware that there are millions of children he has failed to reach. Why should this be?
Believe me, my aim is not to sell more books. With the election approaching, every politician bangs the drum about inequality. But reading, which is still, in essence, free of charge, should be the one activity that puts everybody on an equal footing. How have we allowed it to become the pastime of a privileged few?
Taking up the challenge
It also troubles me that we seem to have come full circle. To some extent, narrative fiction was reinvented by J K Rowling - it's hard to believe that children weren't challenged by books that stretched to 760 pages - and a phalanx of writers crested on her success: Michael Morpurgo, Philip Pullman, Jacqueline Wilson, Malorie Blackman, Eoin Colfer, Darren Shan.and me. Today, it is Jeff Kinney (the Wimpy Kid series) and David Walliams who top the bestseller lists, with books that are witty and entertaining but nowhere near as ambitious.
Speaking personally, I was a little sad when, in Walliams' Gangsta Granny, we were told that among the old woman's vices, which also included dribbling and farting: "Her house was stuffed full of books and she was always trying to get Ben to read them, even though he loathed reading."
The idea that children automatically dislike reading or that books belong to a more fusty, ancient generation is patently absurd. Brightly re-jacketed and with some of the more arcane references (Rubik's Cube, Alex Ferguson, the Sony Discman, flares) removed, it seems that Alex Rider is as popular as ever.
Quite recently, I addressed an audience of largely unpublished writers in New York and I stand by the advice that I gave them. Write up for children, not down to them. Despite my misgivings about the general direction of narrative fiction, look at what Patrick Ness is doing in book after book. Or look at John Green. There's no farting or giggling in The Fault in Our Stars but it has still sold 10 million copies. We don't need to be afraid of powerful stories or serious ideas. The audience is there.
What children don't have is time. It seems to me crazy that the national curriculum has crowded out reading for pleasure. Why are so many school libraries underfunded? Why is it not statutory for every secondary school to have a trained, full-time librarian?
But there I go again. I'm just a writer. What do I know?
Anthony Horowitz will be taking part in a live webcast at 11am on 23 April as part of the Scottish Book Trust's Authors Live programme. For more information and to submit questions in advance, visit www.scottishbooktrust.comauthors-live