Anthony Horowitz at the London Book Fair

It’s just as well Anthony Horowitz talks fast. The Literary Café is packed to bursting with his fans and when Lindsay Mackie of English PEN asks for questions from the audience, hands shoot up all over the place.

Horowitz begins by confirming that sad news that there will, indeed, be no more Alex Rider books. But there will be one more book from this universe. He is planning a novel showing the young life of the assassin Yassen Gregorovich, and taking him to the point, at the end of Stormbreaker, where he fails to pull the trigger to kill Alex.

Horowitz says that it took him, ‘about five seconds’ to decide to write the Sherlock Holmes sequel, Road of Silk, despite being well aware of other YA writers who had failed to make the transition to adult books.

He has started to question whether, now his own children are adults, he ought to still be writing for children. “Perhaps it’s time for my generation of writers to step out of the way and make room for a new wave.”

He is passionate about the stripping away of the schools library service, which he sees as an even bigger issue than the shutting of public libraries. And he speaks movingly about his work with young offenders in prison.

In response to Mackie’s skeptical query, he insists he really was given a skull for his thirteenth birthday. (“I’m not sure if it’s weirder that I asked for a skull or that my mother went out and bought one for me.”) It sits on his desk to remind him that his time is not infinite. The plan, he says, is that he will end up the same way, to make a pair of bookends.

He shows us the fountain pen and spiral-bound notebook in which he writes all his first drafts, before switching to a laptop for subsequent drafts, "and to become an instant expert in every make of German machine gun, or whatever." The sound of a pen scratching across the paper keeps him connected with writers of the past, he says, and he doesn't want "Bill Gates or anyone else coming between me and the creative process."

Intriguingly, he lets drop something that could keep the cryptographers among his fans busy for decades. His books are apparently littered with purely private jokes and puzzles – hidden names, anagrams, first letters of sentences that spell out something...

“I’m on my own working for ten hours a day – I have to have something to keep myself amused,” he says, before going off to tackle a lengthy line of autograph seekers.