The seals have been broken, the doors thrown open and, from midnight, the young wizards were devouring the latest derring-do of their hero under lamps on the streets of London. It is, officially, the last occasion that the capital will witness such commercially manicured frenzy. Harry Potter has been retired – to live out his fictional days in the sunset of prosaic adulthood and a wizard’s pension. But can he remain silent for evermore? Will his fans (and his publishers) not harass, cajole and besiege his creator to insert anew sheaf of paper in her computer, open a new file and begin: “Chapter 1. Harry was now 27. . .”

Conan Doyle relented. Sherlock Holmes did not, after all, die a horrible death in the Reichen-bach Falls, but, caught on a ledge, was able to make his way back to Baker Street. Ian Fleming, reportedly, tired of Bond who disappeared at the end of one novel and was presumed dead. Indeed, M went as far as authorising an obituary to be published in The Times.But 007 was too resilient: You Only Live Twice marked his resurrection.

Others have fallen silent because their creators shuffled off this mortal coil. Thomas the Tank Engine might well, like Dr Beeching’s victims, have puffed no more, had not the Rev W. Aw-dry’s son heroically lit a new fire in his firebox. The awful finality of Rhett’s admission that he didn’t give a damn was, with the publication of the sequel to Gone with the Wind, no longer the last word. We also now know, thanks to The Willows in Winter, that Toad did not live happily ever after in a liberated Toad Hall but fell prey again to his craving, this time for a biplane.

The sequels, prequels and attempts to equal the classics are fun but futile. When the curtain comes down, the hero must lie down. The Carry On films carried on far too long and most of the actors were carried off the set. A limited edition increases the value. Would each of E. M. Forster’s novels be a classic had he written another 20? Should we not applaud John Cleese and Con-nie Booth for leaving Basil and Sybil in Fawlty Towers after only 12 episodes? The message to J. K. Rowling is clear: stop now!